503 Won't fire

[Bandit 286]

Well after 20 years and 1100hrs. My 503 will not fire. At first it kept flooding, took the carb bowls off. Rear float in the front carb was sunk. Replaced both floats. Yesturday I tried starting

it but it would not fire. Pulled the plugs, both rear plugs full of fuel. Tried starting it again, would not fire, pulled plugs, rear plugs full of fuel. Opened carb bowls, fuel level looked good, turned fuel on, pushed up on needle valve fuel shut off. I'm thinking ignition problems. How do you test the ignition system? I think I might be flooding it from pulling the rope so much trying to start it. That's what makes me think it is a ignition problem. In 20 years of flying my Avid I have only had to pull the plugs 2 or 3 times because of flooding.

[TJay 1041]

Did you replace the plugs of just dry them off,

[1avidflyer 1983]

If I was at my wits end, I would shut the fuel off, drain/empty the float bowls, pull it through with the plugs out a bunch of times to make sure it was cleaned out, put in new plugs and either prime it or a blast of starting fluid and crank it over to see if it will fire at all.  If it don't fire then, I would say it must be ignition.  This is my first thought, maybe I'll say something different after giving it a bit more thought (or not) ;-)  I'm guessing you have it really loaded up with fuel from the bad floats or maybe the new floats are bad to.  Jim Chuk

[lostman 198]

I have almost always tested ignition systems with either a known good spark plug or a clamp style tester. Just stick the plug somewhere (or use an alligator style clip) to something that is grounded. Pull it over while watching the plug for spark. If you don't hear or see it, it's likely not working. That's when you get a "helper" involved. Preferably someone that you may not want to see around too much for a while or ever, then have them hold the plug and spark plug wire while touching something grounded on the plane. 

When you pull the rope this time it will be audible if the system works. Your soon to be ex-good buddy will hoot n holler like no other. If the audio part of this spark plug tester doesn't work you have other problems. 

[C5Engineer 1170]

I've had this happen with my old 503 as well. If you haven't already put in a brand new set of plugs and try it. Don't know what it is but when they are done they are done. Not unheard of but pretty rare for the triggers to got bad. 

[TJay 1041]

And if all that don't work and you still cant get spark, Un hook your ignition switch and try to start it. But under the circumstances with the bad floats you had, I would lay money on it that it is not electrical.

[ChrisBolkan 130]

I vote NEW plugs. Several times in the life of my 582's plugs got drenched with fuel b/c engine is upside down. Once drenched they NEVER worked again no matter how well I dried them. Don't know why...a mystery to me, but that is what would happen. New plugs ALWAYS solved it for me.

[Bandit 286]

It still will not fire after installing the new floats. Cleaned the plugs. After wearing myself out with the pull rope I pulled both rear plugs, both full of fuel.  I would think it should at least fire. Chris I will order new plugs and try that first. I will also unhook my on off switch and leave it hot then try to start it.

[akflyer 1427]

If they are full of fuel it won't fire.  One thing the ducati ignition is not good at is putting out a really hot spark.  check plug gap too.  If my plugs get worn and the gap is more than .018 then I start getting misses and hard starts.  Plugs are cheap, I probly change them every 15 or 20 hours as I run slightly rich on the oil and never clean them just replace.  In the grand scheme of things, 15 bucks for plugs is cheap to me to replace versus an engine not starting in the middle of no where or quitting on me..

 

[Bandit 286]

I know the plugs will not fire when they are full of fuel. Good advice about changing plugs. That will be the first thing I will try. What is the gap for Iridium plugs and the standard plugs? I agree plugs are cheap insurance. I have run them 50 hrs before. You are right Leni I will only run them around 20 hrs from now on. I don't think these have many hrs on them though.

[akflyer 1427]

I set them at .016" max is .018"

[Bandit 286]

The weather finally broke today, it got up to 25 degrees so I worked on my airplane. I remembered I had a set of new plugs in the baggage compartment so I put them in.  Two shots of prime and three pulls it fired and started. The weather wasn't real good so I just flew around the neighborhood a couple of times then landed. It seemed to run good. I am Going to take your advice  Leni and change the plugs every 15 to 20 hrs like I used to do. Hopefully this cured my problem. Time will tell. Thanks for everyones help.

[TJay 1041]

In My option the 503 is one of the best motor there is, It really doesn't have enough hp to hurt itself, Just struggles on over weight planes.

[Bandit 286]

TJay I agree with you 100%. My 503 has been a great engine so far, but I have to run it pretty hard to make my Bandit fly nice. For the flying I do it works great. The installation is so simple. Not much to go wrong, overall a super engine. To bad the LSA movement killed them.

[akflyer 1427]

What did your plugs look like when you pulled them out.  If you could post pics of them I would appreciate it. 

Glad it was something as easy as a new set of plugs to get you back in the air!  I ALWAYS have AT LEAST one set of extra plugs in the plane.  Too many times I have been on a long flight when it started missing here and there (normally when I would pull power back on a shallow decent).  Land on a gravel bar or beach, change plugs, take a leak and go on about the flight with the lil 582 humming happily away.  The ducatti ignition does not put out a really hot spark and it is very surprising just how a slightly rich mixture (oil or gas) can put a very light black/ dark brown glaze on the plugs and make it miss.  The same with the plug gap.  I set the them at .016 and anything over .018 and it likes to miss as well.

 

[lostman 198]

Glad to hear it was just the plugs! Too bad the issue fought you for a bit, but that it was remedied very easily. 

Kenneth

[Bandit 286]

Well I might still be chasing my problem. Went out tonight and could not get it to fire. Pulled the new plugs. Rear plug in rear cylinder was the only plug that was full of fuel. Had the gap set at .018 , changed the gap to .016. Then it started right away. Maybe I had the gap set to wide. I'll find out next time I fly. At idle the engine would speed up slow down until I richened the mixture. Then it ran good, but at cruise speed it was running rich. I could feel the thumping in my rudder pedals. Do I need a bigger main jet? I could then lean it out at cruise and idle would be richer. These are the Iridium plugs I replaced.

[akflyer 1427]

I don't think the main jet is the issue.  What happens if you drop the needle a clip to lean out the cruise? 

I have had my arse kicked more than once by just a few degrees change in temp and humidity.  When the starts align just right the settings seem to need to be right in between jet sizes etc.  I have 2 jets I run, 165 in summer 170 in winter.  I do use the IFA mixture A LOT to dial in cruise EGT's to keep the rudder pedal thumping down.  When it is -30 or so, the EGT's read WAY off so my feet become my EGT gauge   The gauge shows trend but I dial in cruise with fuel flow and as you said, "thumping in the pedals".  The first time I felt the thumping I was over cook inlet and not at a gliding height and I had the seat cushion sucked up my butt so far it was tickling my throat.  I was scared to play with the dials lest she quit.  When I got to the other side I started playing with the mixture and in one turn of each it cleared right up.  When I got home I checked into it and found that was a normal "tell tale".  This was when I first started flying the Avid with the IFA.  I now don't think I could live without a 2 stroke and having control from the cockpit over the mixture.

 

 

[Bandit 286]

I'm thinking I have the 158 in now. Tomorrow I will check. I have a set of 162. I'm going to try them. I have the Attic Sparrow mixture control also. I also do the same as you Leni , run it rich then lean it out until you get rid of the thumping. I am going to take some pitch put of my prop. Only turning 5900 on take off. At cruise I lean it out until it ran smooth.

 

[akflyer 1427]

was it turning full RPM before this issue started?

[TJay 1041]

One more trick you can do, If you have cht sensors on the plugs put both sensors on the rear plug in each cylinder, what that does is get the rear plug up a little higher in the cylinder, when the plane sits on its tail all the fuel runs to the rear of each cylinder and sits in those plugs, Get them up a bit higher and fuel sits around them instead of in them.

[Bandit 286]

was it turning full RPM before this issue started?

yes I was turning 5900-6000 on take off. If I flatten it out any more I have to run just about wot to get it to fly decent. I need the airspeed to read about 76 mph. If not it flies tail heavy.

[TJay 1041]

One more trick you can do, If you have cht sensors on the plugs put both sensors on the rear plug in each cylinder, what that does is get the rear plug up a little higher in the cylinder, when the plane sits on its tail all the fuel runs to the rear of each cylinder and sits in those plugs, Get them up a bit higher and fuel sits around them instead of in them.

Shit I just read what I wrote, sorry put the cht sensors on the front plugs, that way the rear are up farther, guess that's what happens when you breath poly-brush half the day.

[steveo88 0]

Make sure you have good compression on 2 stroke.How many hours since last set of piston or rings installed?  Regards  Steve

[Bandit 286]

88 hrs on a major overhaul.