Power loss. Off field landing...

[EDMO 1078]

Larry,  A similar question here to go with your 912 vent line info above:  The vent tubes on my 532 were connected together, instead of being vented to atmosphere - Could this be a reason it was quitting?    EDMO

[gregpro50 64]

Yes I just read that as well last night when researching.  Lesson learned.  I don't think the overflow would have killed the carb if it was vented to the atmosphere.  Still a fire hazard but I think I would have still had power.  I hope people take note so the same thing doesn't potentially happen to someone else.  I do see a lot of vents going into the filter on other setups.

[EDMO 1078]

I have read about inspectors who would not approve the vent tubes unless they went all the way outside of the cowl, away from exhausts - That may have been why someone connected my vent tubes together instead of leaving them open to atmosphere?   Probably the builder and inspector didn't know any more about the 2-strokes than I did.    EDMO

[gregpro50 64]

You've got me thinking now.  I had just oiled the K&N filter so it makes sense that it would put even more suction on that vent line drawing fuel right into the carb throat.  At least I would think that saturating the element would add more air restriction which would have to change the pressure differential between the float bowl and the inside of the filter.  I mean I had just oiled the filter the day before.

[Av8r3400 1179]

Larry,  A similar question here to go with your 912 vent line info above:  The vent tubes on my 532 were connected together, instead of being vented to atmosphere - Could this be a reason it was quitting?    EDMO

The tube on a bing 54 carb should be in a loop between the two bungs, but there should be a hole in the tube in the middle to atmosphere.

[Av8r3400 1179]

You've got me thinking now.  I had just oiled the K&N filter so it makes sense that it would put even more suction on that vent line drawing fuel right into the carb throat.  At least I would think that saturating the element would add more air restriction which would have to change the pressure differential between the float bowl and the inside of the filter.  I mean I had just oiled the filter the day before.

The proper amount of oil will add very little restriction to the flow of a K&N filter.  Unless you way over oiled them this wouldn't cause a problem.

[EDMO 1078]

Larry,  A similar question here to go with your 912 vent line info above:  The vent tubes on my 532 were connected together, instead of being vented to atmosphere - Could this be a reason it was quitting?    EDMO

The tube on a bing 54 carb should be in a loop between the two bungs, but there should be a hole in the tube in the middle to atmosphere.

Guess that's where mine was tubed wrong - there was no T, or hole to vent - just connected together solid.  EDMO

[gregpro50 64]

You've got me thinking now.  I had just oiled the K&N filter so it makes sense that it would put even more suction on that vent line drawing fuel right into the carb throat.  At least I would think that saturating the element would add more air restriction which would have to change the pressure differential between the float bowl and the inside of the filter.  I mean I had just oiled the filter the day before.

The proper amount of oil will add very little restriction to the flow of a K&N filter.  Unless you way over oiled them this wouldn't cause a problem.

No.  Just enought to give them a pinkish color.  The oil is in a spray can and you basically just dust the element until it turns pink.  It's just a weird coincidence that I had just oiled the filters.  I did it because it looked like they had never been oiled before.  I just wonder if a combination of the vent setup, just oiling the filter, and a low float could have all come together to cause this.

 

If someone told me to pick the worst spot for a power problem during that flight it wouldn't have been a second earlier or later than when it happened.

[Av8r3400 1179]

Larry,  A similar question here to go with your 912 vent line info above:  The vent tubes on my 532 were connected together, instead of being vented to atmosphere - Could this be a reason it was quitting?    EDMO

The tube on a bing 54 carb should be in a loop between the two bungs, but there should be a hole in the tube in the middle to atmosphere.

Guess that's where mine was tubed wrong - there was no T, or hole to vent - just connected together solid.  EDMO

The tube that comes with the carb kit has a hole in it...

[EDMO 1078]

Larry,  A similar question here to go with your 912 vent line info above:  The vent tubes on my 532 were connected together, instead of being vented to atmosphere - Could this be a reason it was quitting?    EDMO

The tube on a bing 54 carb should be in a loop between the two bungs, but there should be a hole in the tube in the middle to atmosphere.

Guess that's where mine was tubed wrong - there was no T, or hole to vent - just connected together solid.  EDMO

The tube that comes with the carb kit has a hole in it...

Mine just had a brass fitting connecting two tubes.  I didn't see any hole.    EDMO

Edited 15 Apr 2016 by EDMO

[IFMT 36]

Rotaxowner.com is the answer. Anyone running Rotax products should do themselves a huge service and sign up. For $29 you get access to all the info, service bulletins, training videos, etc. Money well spent. Or you can listen to opinions, like I have around my neck of the woods, from some that just don't get it. And we know airplanes generate a whole lot of opinions. The vent line issue is a classic example of a very specific issue with a very specific routing as stipulated from Rotax. Definitely do not vent this line outside the cowling where it will become a venturi. 

[gregpro50 64]

A very interesting NTSB report showing a forced landing due to the carb vents being installed into the air cleaner.

http://www.asias.faa.gov/pls/apex/f?p=100:17:0::NO::AP_BRIEF_RPT_VAR:ERA14LA089

And another one because the vent lines ran up on top of the carb.  Rotax states the lines have to be installed in a constant decline.

http://www.ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20101207X53535&ntsbno=ERA11LA079&akey=1

My vent lines came from out the carbs, then ran uphill into the air filter.  I wonder if this had any influence on the power loss I had.

 

[Fly-n-Low 181]

 

The tube that comes with the carb kit has a hole in it...

Mine just had a brass fitting connecting two tubes.  I didn't see any hole.    EDMO

There is one there. I didn't realize there was one as all the lines were rotten when I got mine. With no vent it would flood like crazy. I ran in circles until I pulled the vent lines off and DOH!!!

[Fly-n-Low 181]

I hope Doug hasn't seen this because he'd kill me for doing this to his plane.

He is probably going to be like me: Glad  you are in one piece and were able to walk a way!!!

That is a shame though. I am sure you'll get it all fixed though. Doesn't look that bad.

Edited 15 Apr 2016 by Fly-n-Low

[dholly 718]

Rotaxowner.com is the answer. Anyone running Rotax products should do themselves a huge service and sign up. For $29 you get access to all the info, service bulletins, training videos, etc. Money well spent. Or you can listen to opinions, like I have around my neck of the woods, from some that just don't get it. And we know airplanes generate a whole lot of opinions. The vent line issue is a classic example of a very specific issue with a very specific routing as stipulated from Rotax. Definitely do not vent this line outside the cowling where it will become a venturi. 

Best comment so far, I would only add the following...

The subscription fee covers the video library series content primarily, you don't have to subscribe to have access to a tremendous amount of technical information. Service Letters/Bulletins, engine installation and operating manuals that include important information such as the Rotax recommended carb vent line routing for a specific engine/carb has always been free at www.Rotax-Owner.com .

[dholly 718]

So sorry Greg. As with everyone, I join in thanking the KF Powers That Be One for no injuries. The only other silver lining is in trying to learn from your experience.

One thing we do know for certain, the Rotax 912ul w/ Bing 64 carbs installation requires venting the carbs to an atmospheric pressure equal to the carburetor intake. Vent lines must terminate in a ram-air and vacuum free area or be routed into the airbox. This is so important that Rotax repeatedly reinforces the requirement with several separate, big and bold 'Notice' and 'Warning' graphics in the manual. These can be found in the most recent BRP-Powertrain Installation Manual Chap. 73.00.00 Fuel System Section 2.1) Requirements on the carburetor and 2.1.1) Drainage piping on airbox and drip trays and Chap. 73.00.00 Air Intake System Section 3.2.4) Airbox. (Note: there have also been several subsequent Chap. 73.00.00 revisions, including Pages 13 and 14 applicable to the vent lines. All of which are available for free at www.Rotax-Owner.com)

The Rotax airbox has nipples to accommodate the vent lines, however, not all installs (E-AB or S-LSA) use the factory airbox. In fact, Rotax does not require use of their airbox, nor do they specify or care how an aircraft manufacturer achieves their requirement. Only that you do, and that is the purpose of their warning. If your installation uses an air filter on each carburetor ie., without an air box, the carbs are set up from the factory with vent lines terminating at the carb and secured by the float bowl bail. This of course, places the vent lines directly over the hot exhaust. Brilliant. Rotax does make an under carb drip tray that can be installed without an air box. It is part of the Rotax 914 package (Rotax Part No. 874 300), but it can be purchased separately and installed on the 912UL and 912ULS engines.

I choose not to install the drip trays because I never heard of any fuel leakage from the carbs, only from the vent lines, and I didn't think fuel dripping or running out of the vent lines when terminated at the carb and secured by the float bowl bail would necessarily or conveniently follow a path directly into the drip tray. For instance, unlike a tightly cowl'ed aircraft using air baffles, I figure the wide open under cowl area combined with the KF cowl air intake and exit design may create sufficient air turbulence that fuel would end up everywhere in flight. Actually, always made me wonder just how 'equal' the air pressure would be anywhere under a KF cowl when choosing a termination point for the vent lines, eh?

In any event, after a bunch of research and thinking on the issue and with fire prevention foremost in my mind, I opted to do what many others do and terminate the vent lines in the air filters. That removed the primary fire concerns and there is little doubt in my mind that it reduced any air pressure differential to a minimum. I never saw any posts about any specific engine out incident(s) caused by doing so, or any blatant condemnations for this practice on the Rotax Owner Forum where many licensed iRMT's offer their recommendations and back them up with their credentials and real-life practical experiences. Right or wrongly, I presume anything downright stupid or they felt would be interpreted as inappropriate by Rotax would have produced a blaring safety warning.

The one caveat... this was before all the B.S. about defective floats. Not really sure if fuel venting into the filter can be proven as definitively causal in this incidence but it sure is reason to think (or re-think) about the practice. Let me know if I can help with anything.

[gregpro50 64]

Great info Doug.  I appreciate the help.

[gregpro50 64]

FAA meeting tomorrow.  I'm a little nervous.  Maybe from being in business for myself I have a cynical outlook on government agencies and I wasn't born that way.

[1avidflyer 1983]

I've dealt with them several times, and my advice is be honest, respectful, and let them do most of the talking.  It's not as if you groundlooped it and balled it up that way, you had an engine out and were able to fly the plane to where you walked away unhurt.  Most of the FAA guys I've talked to over the years have been very descent.  Some of them are not real familiar with experiment aircraft though.  One didn't realize I could legally do all my own work.  Jim Chuk

[Bandit 286]

You've got me thinking now.  I had just oiled the K&N filter so it makes sense that it would put even more suction on that vent line drawing fuel right into the carb throat.  At least I would think that saturating the element would add more air restriction which would have to change the pressure differential between the float bowl and the inside of the filter.  I mean I had just oiled the filter the day before.

The proper amount of oil will add very little restriction to the flow of a K&N filter.  Unless you way over oiled them this wouldn't cause a problem.

When I broke my 503 in for the first time I over oiled my filters. I could not get it to run right, finally figured it was running way to rich because of to much oil on the filters. Cleaned them out then got it to run good. Now after I clean them I just install them and let the oil from the gas coat them.

[Av8r3400 1179]

An un-oiled K&N filter has almost no filtering properties to it.  

I prefer using the bottle oil as opposed to the spray.  One drop per pleat, it will soak through the dry media quickly and you are set.

[Bandit 286]

An un-oiled K&N filter has almost no filtering properties to it.  

I prefer using the bottle oil as opposed to the spray.  One drop per pleat, it will soak through the dry media quickly and you are set.

May be true for a 912, but in a 2-stroke with mixed gas the cleaned filters will be the same color as the oil that is mixed with the gas after a few minutes of running.

After You've got me thinking now.  I had just oiled the K&N filter so it makes sense that it would put even more suction on that vent line drawing fuel right into the carb throat.  At least I would think that saturating the element would add more air restriction which would have to change the pressure differential between the float bowl and the inside of the filter.  I mean I had just oiled the filter the day before.

The proper amount of oil will add very little restriction to the flow of a K&N filter.  Unless you way over oiled them this wouldn't cause a problem.

When I broke my 503 in for the first time I over oiled my filters. I could not get it to run right, finally figured it was running way to rich because of to much oil on the filters. Cleaned them out then got it to run good. Now after I clean them I just install them and let the oil from the gas coat them.

[gregpro50 64]

I don't think the filters were over oiled but before they were not oiled at all.  I've used K&N filters on other applications for years and know enough that with the spray you just dust them until you get a pinkish color.  There certainly wasn't oil dripping out of them or anything like that.  I just really question whether a combination of that and the vent line route could have really brought forth a mixture problem due to the atmospheric pressure differentials inside and outside the carb.  In my head I wouldn't think so but when the throttle is opened up all the way those filters are really sucking in a lot of air.  Could it have put some vacuum however so slight to the vent lines and caused an issue?  There certainly does seem to be quite a bit of evidence of prior instances from other aircraft where vent line routing caused power loss.  Just Google Rotax 912 vent line power loss and there is all kinds of issues with it.  Ground runup was completely uneventful and it was run a good long time to bring it up to 120 degrees but at lower power settings.  The short full throttle runup on the ground wasn't enough to show the issue.

Another interesting point is that the original builder of this plane who was an A&P had issues with the engine cutting out in flight during the testing phase and after several calls to Rotax it was determined that the vent lines he installed were too long and after they were cut back to 4" it ran perfectly.  All of this is in the logbooks.  Of coarse this was back when the engine had the original carb heater airbox setup.  It was only in recent engine hours that the heater box was removed and the filters with the fuel vents added.  Could these vent lines be that sensitive?  I'm starting to think yes.

[dholly 718]

I know you want answers but lets slow down a bit here. Speculation is less than worthless.

1.) "I don't think the filters were over oiled but before they were not oiled at all."

The filters were purchased, received and installed several years ago. Bought off eBay or Amazon, I can't remember anymore but you may have the receipt. As I did not have proper filter oil on hand and the sale did not mention a supply of oil, I contacted the vendor who indicated they were sold lightly pre-oiled without additional reserve oil. To be honest, my initial impression upon receipt was uncertainty whether they had been pre-oiled or not. They were very clearly not soaked (been there, done that, like Mark had to fix that). But then, they did not look or feel totally dry to me either. I have used and oiled KnN filters in the past so not totally ignorant but I ended up convincing myself they may have had a very light oiling at best. There were other more pressing items on the To Do List and I never had the opportunity to either clean or oil them after install.

2.) "I just really question whether a combination of that and the vent line route could have really brought forth a mixture problem due to the atmospheric pressure differentials inside and outside the carb.  In my head I wouldn't think so but when the throttle is opened up all the way those filters are really sucking in a lot of air."

Terminating the vent lines into either an airbox or air filter (doesn't matter to my thinking) results in a more equal atmospheric pressure differential, IMHO. If the Rotax requirement is to be as equal as possible to the air entering the intake throat (not entering the airbox or filter), how could it not be preferable to hanging in the breeze under cowl somewhere? Even if proper length vent lines are terminated at the carb and secured by the float bowl bail (which is the Rotax configuration when not using the optional airbox and most likely meets Rotax's ram-air and vacuum free zone requirement for the majority of installations), stands to reason when referring to a KF installation they are subject to significantly more buffeting and other forces that impact and increase atmospheric pressure differential under cowl. I don't think throttle position matters at all if the lines terminate within the airbox or filter, carb pressure is still always going to be closer to the air pressure at the intake than if outside the airbox or filter. I also think if there were any suction risk under normal operating conditions at all, Rotax would not route carb vent lines directly into the airbox.

3.) "There certainly does seem to be quite a bit of evidence of prior instances from other aircraft where vent line routing caused power loss.  Just Google Rotax 912 vent line power loss and there is all kinds of issues with it."

I used your search parameters exactly and concluded the following: every single loss of engine power that may have had carb vent lines in the equation appeared due to improper length of vent line, improperly terminating in a ram-air or vacuum zone and a possible blocked vent line. All of which have -zero- to do with routing the vent lines into an airbox or filter. I went through several pages of search results but if I've missed something, please do help me out. When I researched the topic years ago I never found one single instance where venting the Bing 64 carbs into a 912ul airbox or filter of any kind caused so much as rough running, let alone was blamed or linked to a fire or a loss of RPM due to fuel dump caused by faulty or failed carb float(s). Doesn't mean it couldn't or didn't happen here, there is always a first time, but I sure would be interested in any FACTS or empirical data that confirms it actually happened before.

I agree the issue of carb venting must be taken very seriously, it has been demonstrated many times just how sensitive and important the Rotax venting requirements are. The first flight of your plane is perfect example of why proper vent line length when terminated to atmosphere under cowl is critical. That entry sure got my attention! I don't think removal of the carb heat airbox is a factor, guessing the majority of 912 installs in KF airframes omit it due to cowl and carb location. However, that is completely different scenario and question than routing vent lines to an airbox or airfilter. These engines are installed in so many different airframe/cowl/pusher/tractor configurations Rotax necessarily leaves it up to the plane manufacturer to meet their requirements (ram-air and vacuum free zone) in whatever way they so choose. Rotax specifically recommends and provides provision to vent carbs directly into their airbox. My Aeropro has carb vent lines into the airbox, as do many other SLSA's. 

If Rotax finds routing vent lines to an airbox a preferred method, is routing to a filter appreciably different or problematic? Nowhere in any Rotax BRP-Powertrain install, operation or maintenance manual does it prohibit or direct against venting carb lines into a round or conical filter which, of course, are Rotax approved air filter configurations that Rotax also provides. The way Rotax ALWAYS errs on the side of caution, it they believed that somehow it was ok to vent lines into their airbox but for whatever reason venting into a non-oem airbox or particular or different style filter was a liability waiting to happen, you would think there would be an big fat Notice or Warning box in the manual(s) somewhere.

Well, after some further thought and with benefit of now owning a plane with an airbox, I think maybe there is a caution to note. Here's why: not sure precisely how the Rotax airbox works but on my Aeropro airbox, the vent line nipples enter thru the side of airbox to the outside the filter media. Therefore, anything coming though the vent line has to make it's way past the filter to enter the intake throat. If you route a vent line into the backside of a round or conical KnN filter, you enter to the inside of the filter media. Therefore, an unrestricted path to enter the intake throat. Obviously two different installs that -may- react differently to a possible fuel dump caused by a bad float. Not trying to argue anything, but is a vent line even large enough to deliver a sudden fuel dump into either airbox or filter in an amount sufficient to cause an immediate and large loss of RPM? Let's say fuel makes it's way into the KnN filter via the vent line which enters in the lower portion of the filter below the intake throat. At the time it enter the filter I presume it is a solid stream, rather than atomized. So does gravity cause it to fall and pool or be absorbed by the filter media, or does it get sucked upwards into the intake throat? Is that even possible? I have no clue how much suction force that would take, other than I would guess a lot more for a free flowing filter and less for an obstructed filter. Does anyone know for sure?

I also found some interesting info on the float failures. A soggy float, at least as far as I've read, doesn't generally manifest itself in the form of a catastrophic failure, suddenly and completely all at once without some foreshadowing 'tells'. Most posts I found discussing failed floats included comments suggesting they were alerted by odor or rough running, as opposed to total or significant loss of RPM. Heck, some with intermittent symptoms even continued to fly before completing their diagnosis, yikes. So, no prior fuel odor on the ground or in flight? No prior evidence of fuel saturation on the filter element? No prior unusual or erratic engine RPMs? No prior engine miss at all, at any RPM? No prior evidence of fluid, fuel or condensation, noted in the clear vent lines during pre-flights? That would seem unusual to me, but I'm no expert even with 20/20 hindsight and just thinking out loud. You may never know with certainty exactly what happened, can't let it eat you up.

[wypaul 448]

I do not see the spring that helps to support the carb in your photo.  Did it get disconnected in the crash or was it not installed?  With bad floats in my 912 the engine ran rough at idle but would smooth out at full throttle but I was not venting the carbs to the filters.  If the float/s were at fault it will show up when you weigh the floats.