As I believe your Becker ATC2000 is about the same as my Microair 2000, I would recommend removing that 3Â¼ Slip indicator, and use a reducer plate in it's place to mount the transponder. Then use an add-on Slip indicator mounted on the bottom of the Airspeed indicator.
Edit on 27 June: My mistake, I confused it eith other 2Â½ units, and also just noticed the slip indicator ia 2Â½ also.
Actual engine failures are rare. Almost all so called "engine failures" are
returned to service without ever working on the engine itself. It's the
systems which support the engine that usually fail and fuel systems fail
more often than all other things combined. Most of those failures can be
easily prevented and this article will show you how.
RON and MON are two slightly different methods used to determine gas
octane. European countries use the RON method only. Our American
pumps have a label on them which shows that the advertised octane was
calculated as RON plus MON divided by two. If your engine manual says
to use 91 RON then you can use American 87 octane gas since its the
same thing as 91 RON.
Aviation fuel is often called 100LL. It is 100 octane but the low lead part
is misleading. It does have less lead than aviation fuel once had years
ago but it still has much more lead than any automotive gas. That lead is
hard on our type engines because it fouls plugs and causes rings to
stick if we use it on a regular basis. A few gallons of aviation fuel once
in a while doesn't really matter much but I still avoid it as much as I can.
Some "experts" claim that the volatiles evaporate out of gas so fuel
goes "stale" fast. There is a tiny bit of truth in that but it certainly
happen very fast. How long does gas have to sit in your car or lawn
mower before you notice any difference? In my plane 3 or 4 weeks
certainly doesn't cause any problems and I have gone twice that long
with only a very minor difference in performance ... and I even premix
the oil with my fuel. Don't get too paranoid about "stale" gas.
Gas picks up small flakes of rust and dirt as it is pumped hundreds of
miles through underground pipe lines. Slugs of water are inserted into
the pipeline between different shipments and some of that gets mixed
with the gas as it travels through the pipe. Large storage tanks at your
local pipeline terminal always have some water and crap in them. Even
the truck that delivers gas to your local gas station may contribute and
of course water and crap in the gas station tank gets stirred up when the
tank is filled. Gas companies try to filter the gas and most even have a
filter right at the gas pump nozzle but some water and crap ALWAYS
gets to our tanks. A lot of fuel problems happen shortly after refueling
from a new source and even airports can have contaminated fuel.
Some pilots filter the gas going into the tanks on the plane with chamois
cloth, felt or a Mr. Funnel. It doesn't matter what you use or how careful
you are to avoid condensation in the tank sooner or later there will be
water and crap in your tank so you should plan for your fuel system to be
able to handle some of it.
ELECTRIC FUEL PUMPS
The Mikuni pulse pumps are designed to suck fuel up to the engine and
can easily handle the 3 or 4 feet of vertical lift needed with our engine
and tank locations. Faucet recommends mounting electric pumps below
the fuel tank because they can NOT produce much suction.
Many people think that an electric fuel pump will provide an extra margin
of safety. That's okay but make sure that you understand what you are
doing or you can wind up LESS safe. Dual pumps can be used safely
but you need to do it correctly.
If you use pumps in series each pump must provide enough fuel
pressure by itself in case the other pump fails. The second pump can
boost the pressure of the first pump so high that the carb inlet needle
valve can't close and then fuel will squirt out of the float chamber vent.
prevent that you need a pressure regulator ... but then you depend on
that ONE regulator to stay in the air. Wasn't your orginial concern that
you depended on ONE fuel pump? Pumps in series usually add more
potential problems than they remove. I do NOT recommend series use.
For parallel use we usually use the Facet 40104 or 40105 4PSI pump
when the pump is in the wings and the Facet 40106 6PSI pump when
the pump is mounted low in the plane so that the carb sees the correct
pressure. NONE of those models have a check valve built in so any
time there is more pressure at the outlet port than is being created by
the electric pump fuel will be forced backwards through the pump. If
the electric pump gets turned off then a large part of the fuel flow from
the Mikuni pump will flow backwards through the electric pump.
With engines mounted high and fuel pumps mounted low even with no
pumps running there is one PSI pressure on the pump outlet port for
every 37 inches in height just from the head pressure of the fuel in the
line up to the carb. For this discussion call that 1 to 2 PSI head pressure
at the electric pump outlet when all pumps are off.
Fire up the engine and the Mikuni will add 4 to 7 PSI on top of that head
pressure to give about 5 to 9 PSI total at the electric pump outlet. The
electric pump can only pump 6 PSI so fuel from the Mikuni can flow
backwards through the electric pump at high engine speeds EVEN
WHILE THE ELECTRIC PUMP IS TURNED ON.
Electric pumps can force fuel backwards through the Mikuni pump too if
it has grit in the internal flapper valves. Reverse flow can cause fuel
starvation and other problems like unexpected fuel transfer to a different
tank depending on how the pumps are connected.
McMaster-Carr sells a good check valve to prevent reverse flow. Part
# 7775K51 only takes 1/3 of a pound of pressure to open and it has a
Viton seat which is rated for gasoline but you need two # 44555K131
barbed adapters to install one in our fuel line. I strongly recommend a
check valve on each pump outlet anytime there is more than one pump
in the fuel system. I also recommend a fuel filter on each pump inlet so
if one filter stops up the other pump can still provide fuel.
If you provide a seperate fuel tank dip tube and fuel filter for each pump
you can have two completely independent fuel systems as long as the
two systems don't connect together except on the carb side of the check
valves. There you can use a 4 port manifold, a cross fitting or two tees to
provide for one line from the electric pump check valve, one line from the
Mikuni pump check valve and two lines to the carbs.
MIKUNI PULSE OPERATED FUEL PUMPS
Two stroke engines use the piston to suck the air/fuel mixture from the
carb through the intake manifold into the crankcase each time the piston
moves toward the combustion chamber. As the piston moves away
from the combustion chamber the mixture in the crankcase is pushed
from the crankcase into the combustion chamber through the transfer
port. This creates a small vacuum and then a small pressure inside the
crankcase which we call a PULSE. A connection through the crankcase
wall is connected to a chamber inside the fuel pump by a piece of
tubing so the fuel pump diaphram can be moved by these pulses.
Condensate forms when warm fuel/air vapor hits the cooler pulse line.
If that condensate can not drain back into the engine it will collect in the
pulse line or the fuel pump pulse chamber. Fluid trapped in a pulse line
will weaken the pulse at the pump. Fluid trapped in the pump restricts
the diaphram movement. Either one means less fuel gets pumped.
Rotax drills a tiny drain hole in the Mikuni pumps which they supply with
their engines. That hole is located at the pulse port connection to drain
both the pump pulse chamber and the pulse line if the pump is mounted
right side up and lower than the engine pulse connection. Click on the
link below to see how to drill that hole. Some models have the hole in a
90 degree brass fitting at that location.
I don't do that because the hole weakens the pulse and the hole may
get plugged with crap. I mount the pump right side up but above the
engine pulse connection so that any fluid will drain out into the pulse line
and the pulse line will drain back into the engine. Do NOT bolt the pump
solid to the engine. Use mounting which isolates the pump from vibration
and engine heat.
Long pulse lines, leaks in the pulse line and thin wall tubing which can
expand and contract with the pulses also weaken the pulses. Weak
pulses move the diaphram less so less fuel is pumped. Pulse lines
must be less than 18 inches long so the pump must be located near the
engine pulse connection. You can use the engine pulse connection on
the other cylinder to help keep the pulse line short on Hirths but Rotax
only has one engine connection.
It's not easy to do all that so some plane manufacturers take the easy
way out and then problems develop over time after condensate builds
up in the fuel pump or pulse line.
I recommend the large round Mikuni pump since it can pump up to nine
gallons (35 liters) an hour ... but that is only when they are installed
correctly. Remember that they will pump less if they have installation
problems. Both outlets come from the same internal chamber so cap
off one outlet or tee the two outlets together if you only need one outlet.
Its VERY rare to hear of any problem with a correctly installed Mikuni
pump. They have been used on many brands of ATVs, cycles, jet skis
and snomobiles for many years. They don't use electrical power and
they have few moving parts. Those parts are replaced during a low cost
rebuild which is so easy that anyone can do it.
I think they are more reliable than electric fuel pumps so I use a Mikuni
which I replace or rebuild every two or three years and I don't have any
other pump on my plane. If I was concerned I would install a second
Mikuni pulse pump for a backup. Hirth engines have a pulse connection
for each cylinder and there is no reason that you can't use a seperate
pulse pump on each connection. Rotax engines are limited to one pulse
pump since they have only one pulse connection. Do NOT try to use two
pulse pumps on the same engine pulse connection. That will cause both
pumps to recieve weaker pulses and any pulse line problem will affect
FUEL TANKS AND THEIR CONNECTIONS
Be a little leary of fiberglass and other composite fuel tanks. Every once
in a while we hear about a tank which partially disolved because it could
not handle ethanol or some other fuel additive. I suspect the wrong resin
was used to make those tanks.
I don't care what you use to filter your fuel or how careful you are there
WILL be crap and water in your fuel tank. Your first line of defense is to
leave a little room at the bottom of the tank where the crap can settle out
without getting into the fuel lines.
I don't like holes anywhere in a fuel tank except at the top. Sooner or
later holes in the sides or bottom will leak no matter what you do. The
dip tubes described below use a hole in the top of the tank so there are
no leaks. If you already have a hole in the side or bottom of your tank
you should use part #FTG-12240 from Wicks Aircraft. Those grommets
are made of Viton instead of black rubber so they will stand gasoline
service much better.
With no drain on the bottom, you need some other way to get the water
and crap out of the tank. A siphon hose will do that but I use a piece of
1/4"OD stainless or aluminium tubing long enough to reach the bottom
of the tank through the filler opening with enough extra for me to hold as
I guide the probe to the low spots in the tank. 1/4"ID Tygothane tubing
goes over the probe and connects to a squeeze bulb so I can suck out
trash and water. I don't do it everytime I add fuel but I do make it part
my regular maintaince routine. Do it after the crap and water has had
time to settle to the low spots.
Only planes capable of inverted flight need flexible lines inside the tank.
Flexible lines can be a real pain in the butt and may collapse from the
vacuum needed to suck fuel out of the tank. Do NOT try to use them.
Do NOT use screens or filters inside the tank. They will get clogged
sooner or later and you will have a hard time cleaning or replaceing them.
A clear Fram G1 filter at the pump inlet will protect everything plus it's
cheap, eazy to inspect and easy to replace. If you install it with the
on the bottom and the outlet on the top it even tells you when its getting
clogged up. When its new fuel fills the bottom part but the top part stays
full of air. As the bottom part of the filter element gets clogged the fuel
automatically rises to get through the unrestricted partt. Replace it when
the fuel covers the entire element.
The fuel line connection to the tank should be a metal dip tube which
goes through the top of the tank and ends about 1/2" above the bottom
of the tank to keep it above any water and trash in the tank. Do NOT let
dip tubes lay against the bottom or sides of the tank. That can seal off
the open end or let vibration rub a hole in the tank. Fuel will corrode
copper or even brass but aluminium or stainless steel will work fine.
Very large engines might need as large as 3/8 OD X .035 tubing for
dip tubes but 1/4 OD X .032 will easily handle 5 or 6 gallons per hour.
If the tank doesn't have any connections on top install a stainless steel
panel mount coupling through the top of the tank. McMaster-Carr
#5182K375 fits 1/4 OD tubing. It is like a normal tubing coupling except
it has a threaded section in the middle so it can be inserted through a
hole and mounted solidly in place by a nut. If you install a 7/16 viton,
nylon, or PTFE washer as a gasket outside the tank it will seal fumes.
McMaster-Carr #90295A186 is nylon. Use a metal flatwasher between
the gasket and mounting nut to protect the gasket. The tubing nut and
ferrule inside the tank are not used so that the dip tube can be removed
later. The tubing nut and ferrule outside the tank will hold the dip tube
place, seal around it and allow removal of the dip tube. There is a small
shoulder inside the coupling which needs to be drilled out with a 1/4 inch
bit before the tubing will slide all the way through.
Most tanks have a small filler opening so here are some tricks to help
install connections. Large drill bits make a sloppy hole in soft plastic so
drill a small hole then use a tapered hand reamer to enlarge the hole to
the correct size. Don't forget to deburr the hole. Drop a string down
through the diptube hole then fish the string out through the filler
Remove everything from the coupling body then push the string through
the coupling. Tie a weight on the end so the string can't pull out of the
coupling and drop the coupling in the filler opening. The string guides
the coupling to the diptube hole as you pull it out. Install a viton, nylon
PTFE gasket with a stainless flat washer on top to protect the gasket.
Use Locktite when you tighten the mounting nut. Put both pieces of the
ferrule and the tubing nut loosely on the top of the coupling and slide the
dip tube through the coupling to the bottom of the tank. Pull it back up at
least 1/2 inch before you tighten the tubing nut.
A hand pump primer connected to the fuel pump suction line can leak
air into the fuel system if the primer goes bad. I use a seperate 1/4"OD
dip tube just for my primer to avoid that.
A cheap fitting to use for vents in the top of tanks is a metal valve stem
for tubeless truck tires from an automotive parts store. They have a nut
for solid mounting in the top of the tank but throw the rubber seal away
and use a viton, nylon or PTFE washer as a gasket. Remove and
discard the valve core before you slide Tygothane tubing over the fitting.
If you route that vent line below the bottom of the tank fuel will not leak
out if you flip the plane over. If you extend the vent line out the bottom
of the plane it will keep fumes and any slosh overflow out of the cockpit.
I stick a fuel filter on the open end. It keeps bugs out and its my spare
fuel filter on cross country flights. Any vent built into the filler cap
be sealed off to prevent leakage and fumes when the tank is vented
New tanks and lines usually have construction crap left in them which
often causes problems on the first flight. Clean and flush them out
before you trust them.
Some installations with more than one wing tank use a smaller header
tank installed lower than the wing tanks. Fuel drains out of the wing tanks
into the header tank which is then used as the main fuel tank. Header
tanks often have serious problems with leaks so I recommend only an
all metal tank with threaded connections welded in place for every
opening needed. It should also include a welded connection for a drain
valve to drain the water and trash which will collect there. Since the fuel
uses only gravity to drain down into the header tank each wing tank must
have a connection on the bottom and that connection often leaks. You
should be aware that the vent used on the header tank must extend up
as high as the vents on the wing tanks to prevent overflow. Without that
vent, fuel may not drain into the header tank because air trapped in the
header tank will try to work its way up to the wing tanks through the wing
tank drain lines.
FUEL, VENT AND PULSE LINES
Saint-Gobain is a very large company that includes several subsidary
companies, factories and/or divisions. Combined they manufacture
many different kinds of plastic tubing known by several brand names
includeing Chemfluor, Fluran, Norprene, Pharmed, Tygon, Tygothane,
Versilic and others.
Tygon is probably the best known brand name but remember that there
are many different types of Tygon tubing. Most types are NOT suitable
for our application so be sure to check the formulation number. There
are also other companies and they each have their own brand names of
tubing made with different chemical compounds.
Years ago some manufacturers tried to identify their products with
different colors so that buyers could tell a supplier to "Give me 30 feet
of the green stuff". When the "orange stuff" proved to be a better
product or more popular competitors quickly colored their brand orange
too. It quickly got to the point where color tells you absolutely nothing
about what the tubing can safely handle.
Today there are hundreds of different types of tubing available so we
need to understand and correctly use some industry terms. Do NOT
tell a manufacturer that that his product will be used with "gasoline",
or "ethanol" because those mean three completely different things to him
and none of them accurately describe what we really use to him. We use
a 10% ethanol 90% gasoline mixture. Be certain that he understands that
so he can recommend the correct product.
We need a product that lets us easily see air bubbles inside the tubing.
You will see several words used to describe how well you can see
through the tubing. "Translucent" means that you can see light on the
other side but you probably won't see details like air bubbles. "Opaque"
means you can't even see light through it. We need "transparent" or
"clear". Sometimes a color is opaque and sometimes its like the tinting
on your windshield. Its there but you can still see through it fairly well.
We need a product thats flexible. If the minimum bending radius is
more than four or five times the tubing OD then it may get kinked shut
in our application.
We need a product thats soft enough to seal easily on some of our
fittings so it needs to be less than about 90 on the Shore "A" durometer
scale. It also needs to withstand hose clamp pressure so it needs to be
more than about 60 on the same scale.
We need a product thats able to stand a strong vaccum. Mikuni fuel
pumps can suck hard to get fuel up to them through clogged filters.
We need a product that remains stable, resists UV well and lasts at
least 4 or 5 years without getting brittle enough to crack or break with
age and vibration. Most get brittle and crack after a year or two.
My choice is clear Tygothane which is Tygon formulation C-210-A. I
left some on my plane for over 5 years with no problems and it was still
as flexible as when new. I finally replaced it only because the additives
in gasoline had stained it brown on the inside so it was getting hard to
see air bubbles. Tygothane is sold by Lockwood Aviation, Mark Smiths
Tri-State Kite Sales and McMaster-Carr sells it as Part #5549K47 for
1/4ID X 7/16OD. Part #5549K31 for 1/8ID X 1/4OD. They also have
A friend has had simular good results for 3 years with Tygon formulation
F-4040-A but it has a couple of drawbacks. Its tinted yellow so its not
quite as clear. Its too soft for metal hose clamps or twisted safety wire.
It doesn't handle vacuum quite as well and its not made in a heavy wall
size so its not as good for pulse line or pump suction line.
McMaster-Carr sells it as Part #5552K25 for 1/4ID X 3/8OD and
#5552K23 fot 1/8ID X 1/4OD.
Heavy wall tubing should be used for the impulse line and on the suction
side of the fuel pump or vacuum may cause those lines to collapse.
The lines on the outlet side of the pump and the vent lines can be a
thinner wall thickness if you want.
Suction lines should maintain a steep slope all the way from the fuel
tank to the fuel pump so route the tubing to avoid haveing high spots
and low spots. Tiny amounts of water in the fuel can accumulate to
fill low spots and small air bubbles can accumulate into one very large
air bubble to fill high spots. A large slug of water or a large air bubble
can cause problems.
Automotive type worm gear hose clamps often let air leak into suction
line connections because the small size we need doesn't form a circle
very well. McMaster-Carr sells nylon double snap grip clamps which
work well. Part #9579K63 is typical but get the right size. They also
sell spring steel wire formed into a circle as "constant tension spring"
clamps. Part #5324K61 is typical but get the right size. They also sell
a band tightened by a nut and bolt. Part #5412K48 is typical but get
the right size.
If all else fails wrap two turns of safety wire around the tubing and twist
it tight but don't cut into the tubing.
There is a lot of discussion about fuel filters. Some Cessna pilot
"experts" claim that any small stuff which goes through the gasolator
screens they use is so small that it goes through their fuel pumps, carbs
and engines with no problem. Obviously that has worked for them for a
long time but you need to remember the differences in planes and
Their engines are much larger so they use larger jets in their carbs while
our smaller jets are easier to clog up. The main problem is that our fuel
pumps depend on internal flapper valves being able to seal properly up
to 100 times a second. Grit that gets through screens can keep those
flapper valves from sealing shut properly. Most of us install a fuel
just before the fuel goes into the fuel pump to protect the pump and carb.
Purolator (and others) make a filter with a glass sediment bowl that you
can take apart to replace the filter and clean out the bowl. It works fine
on the pump output and there is no problem with them there.
Unfortunately we need a filter on the pump intake and there is suction
there. You may have already noticed that suction is harder to seal than
pressure if you had a hard time keeping air bubbles from leaking into
your suction line connections. The seal at that filter bowl was NOT
designed to handle suction and if you try to use it on the suction side of
fuel pumps it WILL suck air into your fuel system. Many UL pilots have
known this for years and avoid them but sometimes a newbie will try to
use one then post that he has a problem with bubbles in the suction line.
Some internet "experts" claim that filters should not be used on the
suction side of pumps and use those posts as "proof". You should
remember that many of the "experts" use wing tanks to gravity feed
fuel to a lower engine. Their fuel doesn't need to be sucked up to the
engine so they are not familar with our fuel pumps or the suction needed.
They claim that the bubbles are "vaporizeing" out of the fuel because a
high vacuum is needed to suck fuel through a filter.
It is true that a high vacuum in fuel lines or high temperatures can cause
"vapor lock" when fuel vaporizes but that is NOT what is happening here.
The vacuum used normally isn't much more than we generate when we
suck on a hose to siphon gas and the bubbles are present even when
the temperature is below freezeing. Its real easy to prove that those
bubbles are simply air leaking into the suction line. Replace the glass
bowl filter with any different type of filter and there are no more air
bubbles in the suction line.
These same "experts" have claimed that our other filters leak air into
suction lines. Thats not true. The ONLY reports of air leaks are those
glass bowl filters and tubing connections which use the wrong clamps.
I did see one report where vibration unscrewed one brand of so called
"high performance" fuel filter. They are a metal cylinder which screws
apart so you can replace the very small filter element. I do NOT
recommend them because the elements are too small.
Some fuel filters use a sintered bronze element. That element has a
very small surface so it doesn't take long for them to get cloged up.
I do NOT recommend them.
It's hard to beat the plain old pleated paper type fuel filters which have
been used in cars, boats, cycles and many other applications for years.
I highly recommend them. The Fram G1 is large and clear with
connections that fit our 1/4"ID tubing. Get them from Mark Smiths
Tri-state Kite Sales or from Lockwood Aviation as part #414-3636 if
you can't find them locally.
Some "experts" claim that ethanol in the fuel absobs water and that
water will clog up paper filters. It is true that ethanol absorbs water but
neither gasoline, ethanol, water or any combination of them will clog up
paper filters. Anyone with a paper filter and a squeeze bulb can easily
suck any or all of it through the filter. Think about the millions of paper
fuel filters used in cars for years.
You should trap excess water and trash in the fuel tank before it ever
gets to the filter anyway. Cessna "experts" should think of our fuel tank
as our big gascolator where water and trash settle out. We just use a
filter at our fuel pump intake instead of a screen inside our "gascolator".
Some "experts" claim that its better to use a gascolator because filters
will clog up. The reason filters clog up is because they are doing their
job by keeping stuff out of our pumps and carbs. Rather than clean a
screen we replace filters. As long as we replace filters when they need
replacement there is never a problem.
SQUEEZE BULBS, CHOKES AND PRIMERS
A squeeze bulb will only pump fuel to refill the carb bowls and lines
which have drained down while the plane was sitting. It will NOT squirt
fuel into the intake manifold to help the engine start like a hand pump
primer. It will NOT enrichen the mixture to help cold engines run
smoother like a choke. Some people have had so much trouble with
squeeze bulbs that they refuse to use them. Squeeze bulbs should be
replaced once a year to minimize problems like splitting, leaking,
shedding rubber particles into the fuel or failure of their built in check
valves. I do NOT recommend them.
Our "choke" is actually just a seperate fuel path inside the carb which
allows fuel to flow through a seperate jet. That enrichens the mixture to
help cold engines run smoother but it doesn't "prime" the engine or fill
the carb bowls and fuel lines. I don't use mine at all.
A hand primer pump squirts a little fuel into the intake manifold every
time you pump it. Proper use eliminates any need for a squeeze bulb
or the choke. It does take a little experience to learn how many times
to pump it before starting the engine and when to pump it to keep the
engine running while the carb bowls and fuel lines refill and the engine
warms up a little. I recommend them highly.
I mounted my primer near my right shoulder when I'm seated in the
plane to keep all fuel behind the pilot. That keeps the primer lines
short and lets me reach across and pump it with my left hand to use
it as an emergency fuel pump. I can also reach it from outside the
plane to prime the engine as needed when starting the engine.
To start my plane I lean in to make sure the throttle is all the way back
and the kill switches are in the "run" position. I position myself so that
my left leg is against the front of the right main tire. If the engine were
to rev up the plane may run over a chock but it can't run up my leg
before I can kill the engine. I look over the wing to watch fuel move
through the primer line as I pump the primer. Once it reaches the carb
I give it a couple more pumps to squirt fuel into the engine. The exact
number of pumps depends on my past experience with the plane and
the current temperature. I look to be certain that the area near the
pusher prop and the area in the prop blast are clear then yell "Clear
prop". Last I lean in and hit the starter. It may take another pump or two
to keep the engine running until it warms up. It doesn't take long to learn
when to pump it.
FUEL PRESSURE GAUGE OR LIGHT
I'm a firm believer in KISS (Keep It Simple Stupid) so I won't put one
on my plane but some people like to have a fuel pressure gauge or a
light that comes on when fuel pressure drops below 2 PSI. Thats okay
as long as you understand what you are really seeing.
You need to see the pressure right at the carb inlet. If you just tee into
the fuel line there and run a line down to a gauge mounted on the panel
you will see the head pressure of the fuel in that line added to the actual
pressure at the carb. You need a 10 PSI gauge but normal gauges are
not very accurate near the ends of their scales and can not survive
vibration very long. You have also added the potential problem of fuel
leaks and fire in the cockpit. Electronic sensors for an EIS or a
pressure switch for an indicator light installed near the carb inlet solve
those problems but are they really useful?
If trash blocks the carb inlet needle valve or the main jet the engine will
starve for fuel but the light will never even flicker because there will
be normal pressure at the carb inlet.
If air is leaking into the pump suction line the pump will pump air bubbles
into the fuel lines. The light will never even flicker as small bubbles
through the carb inlet valve and get vented because the pressure in the
the fuel line stays normal. If there is enough air in the fuel line to
the pressure in the fuel line then you won't get much advance warning
from the light before the engine quits.
The most common problem is crud building up in the fuel filter. How
fast that happens depends on how much crud is in the fuel and how
much filter surface area the fuel filter has. Refueling with heavily
contaminated fuel can clog a small brand new filter very shortly after
takeoff. Normal fuel usually takes over 100 hours of flying before
problems ever start. Once the fuel filter can not pass as much fuel as
the engine is useing the fuel level in the carb bowl starts to drop which
opens the float needle valve more. The PRESSURE in the fuel line
starts to drop as the needle valve opens more because the fuel FLOW
is restricted by the fuel filter instead of the float needle valve.
the fuel PRESSURE drops below 2 PSI and the light comes on. Notice
that the engine is still getting some fuel and that fuel FLOW may be
enough for the engine to run for hours. The light tells you that the fuel
PRESSURE has dropped below 2 PSI but thats all it can tell you. You
have no way of knowing why. You have no way of knowing how long the
engine can continue to run. You need more information before you can
make a decision about what to do.
NEVER base a decision to make an emergency landing on an idiot
light alone. That light should only be used to tell you to check the EGT
gauge. The EGT will tell you if your engine is getting enough fuel or not
so base your decisions on the EGT instead of an idiot light.
Heres why. As previously explained when the fuel system can't deliver
as much fuel FLOW as the engine is useing the level in the float bowl
starts dropping. As that level drops the jets deliver less fuel so the
mixture starts getting lean and the EGT starts to climb. As long as the
EGT is normal you have no reason to make an emergency landing. If
the EGT is high you should look for a landing site but also reduce
throttle to see if the EGT will drop to normal when the engine uses less
fuel. If the EGT drops to normal you can limp a long way to a better
landing site at reduced throttle so you don't really need to make an
emergency landing right away.
If the float level drops too far the engine will start surgeing. That is a
short increase in RPM and power when the mixture gets very lean as
the engine runs out of fuel. Once the mixture gets too lean to ignite the
engine coasts to a stop unless it gets another shot of fuel to run or
surge again. The prop windmills for some time after the fuel is gone.
That keeps the fuel pump working so its common for the engine to
surge several times before it quits completely. Now you have a real
emergency but you may still be able to limp to a better landing spot if
you can use the hand primer to help the fuel system deliver enough
fuel and/or reduce the throttle so the engine doesn't use as much fuel.
Most fuel problems show up first at full throttle because the fuel system
works the hardest then. Get in the habit of checking for high EGT during
all full throttle operations such as climbout. When you start to see that
happen, its time to replace your fuel filter and check the rest of your fuel
The pressure gauge, idiot light or EGT will not give any warning of a
sudden serious fuel system failure so you should fly like the engine
could quit at any time and practice emergency landings so you will be
ready for a real one.
FUEL INJECTION CONSIDERATIONS
Fuel injection requires a high pressure fuel pump. Most of those pumps
need a return line to be run from the pump back to the fuel tank because
they use a built in pressure relief valve as a form of pressure regulator
for the outlet port. When the pressure at the outlet port rises higher than
the set point of the pressure relief valve the pressure relief valve opens
to divert fuel from the outlet port to the return port until the pressure at
the outlet port drops back down to the set point.
That means that the fuel flow into the fuel pump is much greater than the
fuel flow required by the engine alone. The return line from the pump
back to the tank and the suction line from the tank to the fuel pump inlet
port must be big enough to handle the maximum fuel flow that the pump
can produce. Note that the fuel filter in the suction line must be able to
handle the larger flow also. The line from the fuel pump outlet port to the
fuel injection can be much smaller since that flow is only the amount
actually used by the engine but that line must be able to handle the high
pressure that is at the fuel pump outlet port.
THE BOTTOM LINE
You should NEVER attempt the first takeoff until you are absolutely
certain that your new fuel system will provide enough fuel under all
conditions. Tie the plane down and run it at full throttle to be certain
it won't starve for gas during takeoff and check closely for leaks. Always
be prepared for the engine to quit on takeoff.
Here's another handy one. The link dosen't seem to work, so I'm pasting it here....
Engine and Prop Adjustments JAN 2010
Picking the right combination of engine, reduction unit and prop is
discussed in a different article. This article tells you how to adjust the
engine and prop correctly after they are installed. Its also a good guide
to things you should check on a used plane and before you first start a
PRELIMINARY CHECKS AND ADJUSTMENTS
A lot of problems can be traced back to inaccurate instruments. It is very
common for tachs to have large errors. Borrow a Tiny Tach or an optical
prop tach and compare readings to check your tach over the whole range.
It is impossible to correctly adjust the prop with a bad tach. Be certain
that your EGT and CHT gauges read correctly. Useing the wrong type of
thermocouples or wire for them is a common mistake. It's also real easy
to enter wrong numbers or settings for electronic displays. See my article
on thermocouples for more information.
Check for water or crap in the carb bowls. Make sure carbs are mounted
square with the engine since a tilted carb can cause one cylinder to run
hotter than the other on some engines. Cracks in the carb mounting
sockets can cause lean mixtures so replace them if they are brittle.
Check for adaquate fuel flow to the carbs. Any time you notice higher
than normal EGT or if the plane won't reach normal full throttle RPM
install a new fuel filter before you waste a lot of time looking for other
problems. See my article on fuel systems for more info.
Each carb has an idle jet, a needle jet with a jet needle and a main jet.
All have tiny numbers on them which tell you the size. Check to be sure
they are the factory recommended jets and the jets are the same in both
carbs because its common to find that a previous owner has installed
different jets. The factory recomendations are almost never wrong so
its very important that the factory jets are used during testing.
Check that all throttle cables are routed to drain out any water inside the
cable outer jacket. Water collecting in a low spot can cause corrosion
or freeze in the winter to lock the cable in one position.
CABLE ADJUSTMENT FOR A SINGLE CARB
Pull the throttle all the way back against the lower throttle stop. Where
the cable enters the top of the carb there is an adjustment that is covered
by a rubber boot. Slide the rubber boot up the cable to get it out of the
way then gently pull upwards on the outer jacket of the cable. There
should be a tiny amount of free movement before you feel the inner cable
start to move the slide upwards. That tiny amount of free play is critical
be sure that the cable is not holding the slide up off of the idle speed
adjustment screw. If you have trouble feeling it you can remove the air
filter and look inside the carb throat to watch the slide move. Loosen the
lock nut and turn the adjustment screw until you have that tiny amount of
free play if needed. Lock the adjustment and work the throttle back and
forth a few times to be sure the cable outer jacket ends are fully seated
in their sockets correctly then pull the throttle all the way back against
lower throttle stop. Double check that the amount of free play is still
correct at the top of the carb before you reinstall the rubber boot.
Push the throttle all the way forward against the upper throttle stop and
look in the carb throat. The slide should go up far enough so that it does
not block any of the carb throat opening. Its okay if it goes up just a
extra but if it goes up too much it will bind and put a strain on the
cable. You should install some sort of upper throttle stop to prevent that.
CABLE ADJUSTMENT FOR DUAL CARBS
Dual carbs must be mechanically matched or one cylinder will have a
higher EGT than the other and/or you can not get a smooth idle. Pull the
throttle back against the lower throttle stop. Where the cables enter the
tops of the carbs there are adjustments that are covered by rubber boots.
Slide both boots up the cables to get them out of the way. Loosen the
locknuts and turn both adjusment screws down two turns. That makes
sure that the cables are not holding the slides up off of the idle speed
Remove the air filters and use the smooth ends of drill bits as round
feeler gages to check the clearance between the bottom of the slide and
the bottom of the carb throat on each carb. Pick a drill bit that will
slide into the smaller of the two openings and use it to adjust the idle
speed screws on both carbs until both openings are the same. Your
carbs are now mechanically matched. To keep them matched you must
ALWAYS turn the idle speed screw on both carbs the same amount
when makeing idle speed adjustments. NEVER adjust just one idle
Make sure the throttle is pulled all the way back then go back to the cable
adjusters on top of the carbs. Screw them out to take out ALMOST all of
the free play. You check that by feeling how much you can lift the outer
jacket before you feel resistance. It takes a delicate touch but you need
just a tiny amount of free play to make sure that the slides are not held up
by the cables when the throttle is pulled all the way back. If the free
is not the same on both carbs then one slide will start to rise before the
other so this adjustment is critical. Tighten the locknuts and work the
throttle back and forth a few times to be sure that all the cable outer
jacket ends are fully seated in their sockets correctly. Double check
that the free play is still correct on both carbs then slide the rubber
over the adjustments. If you have done it correctly both slides will start
to move upwards at the same time and the bottom of both slides will be
flush with the top of the carb throat just before you reach full throttle.
Set the throttle wide open and check that both slides go up far enough
so that they don't block any of the carb throat openings. Its okay if they
go up just a little extra but if they go up too much they will bind and put
a strain on the throttle cables. You should install some sort of upper
throttle stop to prevent that.
INITAL CARB ADJUSTMENTS
Because the jet RPM ranges overlap you should make the idle speed
adjustments first and work up to higher RPMs. If any large adjustments
are made it will be necessary to repeat the idle adjustment procedure to
fine tune all adjustments. Make sure a clean air filter is installed before
There is an AIR MIXTURE adjustment screw which will fine tune the
amount of air at idle speeds only. The IDLE SPEED screw limits how
far the slide can come down to close off the air flow. If you aren't sure
which screw is which you can see the end of the idle speed screw
sticking out inside the carb air inlet if you remove the air filter. A
above the slide pushes the slide down against that screw.
To prevent engine shake and gearbox chatter our engines need an idle
speed of around 2000 RPM so warm up the engine and adjust the idle
speed screw for about 2000 RPM. Remember to turn BOTH idle speed
screws the same amount to keep the carbs matched if the engine has
Adjust each air mixture screw to get the highest RPM at that idle speed
setting. 1/8 of a turn on adjustment screws can make a big difference so
keep the adjustments small. You will have to go back and forth between
dual carbs a couple of times to get the best possible idle because they
As the mixture gets better the idle speed will increase so adjust both idle
speed screws the same amount then fine tune the mixture screws again.
Keep at it until the engine idles smoothly at the lowest speed which has
minimum engine shake. Check the cable adjuster on top of both carbs
after you finish to make sure there is still the same tiny amount of free
play on each carb.
Be aware that it's easy to get an arm cut off by the prop and anything you
drop may go through the prop. I usually tie a short safety rope around my
waist and the base of the wing spars so that I have to stretch way out to
reach the adjusting screws. That way I can't forget and move toward the
prop. Fortunately you won't have to do this again until you notice an idle
INITAL PROP ADJUSTMENTS
Now you need to know how the factory recommends that your engine be
used. For Rotax engines download the operators manual at
The figures used below are for the Rotax 503 so look at page 10-1. If
you have a different engine you need to change those figures to match
your engine manufacturers recommendations. If you have a fixed pitch
prop all you can do is hope that it is the correct prop but all the other
below will still apply.
The Rotax manual lists a "takeoff speed" of 6800 RPM for no more than
5 minutes and a "cruising speed" of 6500 RPM with no time limit.
Its common practice for aviation engines to have a normal operations
limit and a higher takeoff limit so what Rotax should have said was "The
engine can be safely operated at 6800 RPM for five minutes but you
must reduce the throttle to 6500 RPM or less after that."
The RPM that a given engine/prop combination can reach is greatly
influenced by the air speed and any disturbance of the air flow into the
prop. During discussions you will hear several terms used so you need
to understand those terms.
During static testing the plane is tied down. There is no airflow into the
prop so the engine can not reach full RPM.
During the actual takeoff the plane does not reach full speed. There is
reduced airflow into the prop so the engine can not reach full RPM.
During climbout the plane does not reach full speed. There is still
reduced airflow into the prop so the engine still can not reach full RPM.
In addition the use of flaps or even the planes design may block or
disturb at least part of the airflow into a pusher prop.
If you set the prop so that the engine turns 6800 RPM during the actual
takeoff your engine will seriously over rev once you build up more speed
and/or finish the climbout. To prevent that you should adjust the prop to
allow 6800 RPM at full throttle during straight and level flight. This
you the maximum airspeed and keeps your engine below the maximum
factory recommended RPM during all phases of your flight.
Rotax describes 6500 RPM as "cruise speed" but if you actually cruise
at 6500 RPM your engine won't last very long. Its a general rule of thumb
to cruise at the RPM where your engines power curve produces 75%
power for best life. For the 503 thats around 5200 RPM.
Engines are expensive and pilots are cautious so many of them try to
adjust their prop to give lower full throttle RPMs thinking that will be
easier on the engine. That actually works an engine harder because
the prop becomes a bigger load than the engine was designed to
handle. The ignition timing, port timing and carbs are all designed to
work best with the engine loaded just enough to reach the max full
throttle RPM specified by the manufacturer. If you really want to be
easier on your engine simply give it less throttle after the prop has
been adjusted correctly. Loading the engine down so it can't reach
the maximum RPM at full throttle is called "over prop" or "lugging".
It puts an extra strain on all engine and reduction unit moving parts
which will shorten their life.
The first step is to adjust the prop to a pitch where you will have a safe
first test flight. We know that the prop load will be reduced once air is
flowing into the prop at high speeds so the engine will turn faster in
The amount depends on the type of prop, diameter, pitch, etc. To
prevent exceeding the max RPM in the air we need to first adjust the
prop for about 6300 RPM at full throttle while the plane is tied down.
The exact final adjustment will be determined by flight tests later.
Tie the plane down and monitor the EGT and CHT temperatures as you
slowly apply throttle. If the RPMs exceed 6300 before you reach full
throttle, stop and add more pitch to the prop. If you reach full throttle
RPMs stay below 6300 stop and reduce pitch on the prop. If the EGT
exceeds 1150 stop and find out why before continuing tests. If the CHT
exceeds 430 stop and let the engine cool down before continuing tests.
Maybe you need to think about adding some more cooling capacity.
Note that the operators manual lists maximum EGT as 1200 and
maximum CHT as 480 on page 10-1 but we want to stay below those
figures during our early tests.
This is also a good time to watch for surprises like leaks, fuel starvation,
and overheating problems. It's better to find them now than find them in
Prop adjustments and carb adjustments will affect each other so read
this whole section before any test flights and make all the adjustments
in the sequence given below.
During the first phase of first test flights the pilot needs to determine
full throttle engine RPM that is reached during straight and level flight.
should also monitor EGT and CHT closely the entire flight because they
may try to exceed the maximum allowed until the plane has been fully
checked out and the prop is correctly adjusted. After each flight make
small adjustments on the prop until the engine turns very near 6800 RPM
at full throttle during straight and level flight.
During the second phase of flight tests the pilot needs to check the
needle jet and jet needle operation by flying for a couple of minutes at
each of several engine speeds between about 3000 RPM and 5500 RPM.
There will be variations but all EGT readings must be in the normal range.
If most of those engine speeds show a high EGT try moving the clip
down on the needle to provide more fuel for the whole mid range.
Repeat test flights until you find the clip position which works best over
the whole mid range.
You may find a small range of engine speeds which have a high EGT
while all the other mid range speeds are normal. Avoid running in that
small range of engine speeds until all other adjustments are completed.
An incorrect prop or prop adjustment is almost always the reason.
During the third phase of flight tests the pilot needs to check the main
jet operation by watching the EGT during full throttle operation in straight
and level flight. If the EGT gets too high reduce throttle until it cools
down. You MAY need a larger main jet but if the engine could not turn
near 6800 RPM during the test the real problem was the prop pitch.
Adjust the prop and try another test flight.
You may have to tinker a little more with the needle clip to get the EGT
correct over the entire mid range after you have fine tuned your prop.
That may mean some minor compromises but try to keep the EGT as
close to ideal as possible over the most used RPM ranges. Double
check that the final adjustments will not let the EGT run above 1150 or
below 1000 at any RPM.
Remember that air temperature and altitude will have an effect too. I
have to adjust my needle one notch every spring and fall to keep mine
set correctly but four thousand feet of altitude change doesn't change
my EGT enough to matter.
There are four paths fuel can follow to get through the carb. The first is
the choke. Our choke is not an air flow restriction like on cars. Our
is a manual "on" or "off" lever which opens a path for a tiny amount of
extra fuel to flow into the throat of the carb to enrichen the mixture for
better starting. Always turn it off after the engine warms up enough to run
There is some interaction and overlap between the three main fuel paths
but generally speaking, the IDLE JET will control all of the fuel flow at
speeds. The JET NEEDLE is attached to the carb slide and it moves
into and out of the NEEDLE JET. That combination controls almost all
of the fuel flow in the lower midrange, most of the fuel flow in the upper
midrange and some of the fuel flow above that. The MAIN JET provides
the additional fuel needed from the upper midrange to full throttle.
Way too often people jump in and start changeing jets attempting to cure
some problem that isn't really caused by the jets at all. The factory isn't
stupid ... they choose the jet sizes for a good reason and it is very rare
for them to be wrong. Before you even think about any jet changes you
should double check that the prop is adjusted as described above to
provide the correct load on the engine. Maybe your tach reads wrong.
Many jet changes are done by misguided people attempting to get more
speed by adding pitch to the prop. You might get away with a little bit of
extra pitch but if you get weird EGT temperatures or weird fluxuations in
RPM in a narrow RPM range you have gone too far with it and jet changes
won't help much because the engine is overloaded.
If you were able to get a significant speed increase with too much pitch
you will be much better off to use a slightly shorter prop with that pitch
your engine can reach the correct RPM.
Some other things to keep in mind before you tinker with jets.
IDLE JET If you were ever able to correctly adjust the idle mixture then
there is no reason at all to change the jet size. Blow the trash out of it
replace it with the same size.
NEEDLE JET If the midrange EGT temperatures were ever correct
there is no reason at all to change the jet size. It might have the hole
enlarged from wear against the jet needle. Blow the trash out of it or
replace it with the same size.
JET NEEDLE If the midrange EGT temperatures were ever correct
there is no reason at all to change the needle size. It might get bent, it
might get worn in the taper area, it might get worn in the clip grooves on
top or the clip may need adjusting. Replace it with the same size.
NEEDLE CLIP If the mid range EGT temperatures were ever correct
the most it will need is adjustment one notch up or down to allow for
seasonal changes in air density.
MAIN JET If the full throttle EGT temperatures were ever correct there
is no reason at all to change the jet size. Blow the trash out of it or
replace it with the same size.
AFTER THE ENGINE HAS ABOUT 20 HOURS ON IT
Go over all the adjustments above because parts wear together and
cables stretch during their early life. After you get the engine broken in
good it will produce more power and that might mean changes.
After you are more familar with the plane you might consider this trick.
The prop is still producing a certain amount of thrust at idle speed. That
means more "float" distance and longer roll outs which can really matter
in short field landings. After correct adjustment as described above I
back the idle speed screw out a little for a very slow idle. I use a little
of throttle to bring the engine speed back up so the engine doesn't shake.
On final I can pull the throttle all the way back for a steeper but slower
glide. The forward speed of the plane helps the prop windmill fast
enough to prevent engine shake and the prop has a large amount of drag
instead of a small amount of thrust. As the plane slows down on rollout
I add just enough throttle to prevent engine shake. It can make a big
difference in short field landings and more experienced pilots may prefer
That's nicely done, and looks good. But I'd like to indicate a possible problem with the fit of the cowl around the air filter.
During your test runs, up to full power, watch for creasing on the top and bottom of the filter, caused by the cowl and rocking of the engine in it's mounts. This will lead to cracking of the carb boots, which is really bad for the engine. This rocking contact with the cowl may be especially noticeable with a rough idle.