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912ul Sticking Valves and Carburetor questions.

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paul perry

Joined: 11 Jun 2008
Posts: 36

Posted: Wed Nov 19, 2008 5:06 pm Post subject: 912ul Sticking Valves and Carburetor questions.

I have a KFIV with 912ul (I'm not the builder or very mechanically inclined) which has 104hrs on it. It appears I'm having problems with sticking intake valves on the number 1 & 2 cylinders. This was determined with the help of a friend who is an A&P but not familiar with the rotax engines. As far as I know this was not a problem before I purchased it and didn't notice any problems the first 10-20 hrs I flew it. I changed the oil at 95 hrs and instead of the Valvoline 10w-40 semi-syn auto oil and replaced with Valvoline 10w-40 4 cycle motorcycle oil as I though this would provide better gear box lubrication. I also started using 87 octane unleaded with Stabil added. Does anyone think either of these changes could be causing the problem? I am thinking of going back to 100LL (maybe its missing the lubrication the lead provides?). As of right now, if I'm willing to let the engine run extremely rough a few minutes, it will smooth up and run normally. I added Marvel Mystery oil to the fuel (100:1) and ran about 20 gal thru so far. Also, I added seafoam oil additive to the oil about 2 hours ago. The question on the carburetor is this: Both carbs have a 3 inch or so clear tube attached to them right above where the air induction comes in(a little to the side). When I started the engine without the cowl my friend said there was fuel spewing from these tubes and indeed after shutting the engine off they were full of fuel. I would like to know what the purpose of these are and if this sounds like an indication of a problem (possibly caused by the sticking valves)? When I changed the oil at 95hrs it had ran about 35 hrs and oil looked clean (almost new). Also, the  engine had recently been serviced by EAST Troy Aircraft (60hrs) per the previous owner and I have a copy of the invoice (almost $2000) which included a service bulletin on valve spring retainers/carb sockets/and overhauled carbs. Sorry, about the length of this post, but would appreciate the advice from anyone who has a good knowledge of these engines.  Thanks, Paul Perry

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Wed Nov 19, 2008 10:19 pm Post subject: Re: 912ul Sticking Valves and Carburetor questions.

pperrynas,



I have some concerns here.

1. At only 104 hrs. I have some doubts about any valve sticking from a factory delivered engine. What bothers me is how this A&P not knowing anything about the special care and feeding of a Rotax determined the valves were sticking? Did the A&P have the Rotax manuals, did he do a pressure differential test or static pressure test? I might be a little suspicious of my valve spring retainer job until proven otherwise. The engine may have only 104 hrs., but it sounds like an older engine to have the valve spring retainers replaced under that SB.

2. This problems seems to have cropped up after someone worked on the valve system and rebuilt the carbs. 

3. It was good that you switched to a motorcycle oil as it has the right additives for the gearbox that regular car oil does not.

4.  Fuel is not your problem. I would quit mixing all these oils and fuel stabilizers as we don't really know how these mix and what they do combined under high pressure and temps. Use one thing at a time or find out from the Mfg. if it is ok to mix certain fluids. Certainly some fluids are ok to mix, but one detracts from the others properties.

5. Get the carbs balanced and inspected by a trained Rotax person or facility. This sounds like you have a carb issue and a carb problem needs to be ruled out. Use someone that has been Rotax trained and for the time being do not use a regular A&P. 

The carbs are the easiest and cheapest item to check first. 



Definition of an "MIF"?

Mechanic Induced Failure



Nothing against A&P's with Rotax training, but an untrained A&P can be a problem all by itself.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

K Dilks

Joined: 22 Sep 2008
Posts: 108
Location: UK

Posted: Thu Nov 20, 2008 1:30 am Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Just to add to roger good advise , dont use oil additives just use a good bike oil.

 If the engine has sat a long time,sometimes the lead deposits start to come off the piston crown and cause some rough running but a good hard hours use with blow that out. Stick with unleaded.

 

 The carbs need some work as it sounds like the float valvse are a little leaky and /or the float height is out.

 Do a compression check to.

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Back home .................

Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Thu Nov 20, 2008 4:34 am Post subject: 912ul Sticking Valves and Carburetor questions.

Paul,

   I was going to suggest that you contact Roger as he is quite knowledgeable about the Rotax engine. I think he is spot on with his suggestions. The only things I might add are from the training I received at Lockwoods Rotax school a while back (rapidly going bye..bye)

   Stick with auto fuel. 100 LL can cause lead deposits in the oil tank and valve sticking. Keep in mind the alcohol issue which has been brought up many times.

   Rotax does not want you to use any additives,however,Marvel Mystery has been shown useful in the case of valve sticking or no compression on startup as mention by many members on this list. I don't think that would cause your problem.

   You might call a tech at Lockwood to get an opinion. I have found them very helpful with the problems I had with my engine. The instructor at Lockwoods school did mention in class that the most service problems on this engine occur from A & P mechanics. As Roger mentioned, unless they are trained on this engine they can sure (at)#&^% ! it up. Obviously owners can and do also. I highly recommend the school!

   With that said your engine sounds like it is about the same vintage as mine. I have 190 hrs on it and it was delivered in 2001

   I have a neat method of pneumatically syncing the carbs. You can have them synced in about a minute on the Kitfox 4 if you have the yoke throttle mechanism. Give me a call if you are interested. 850-304-7371 (cell)

   I wish I could add more. I had trouble with my engine running rough on throttle reduction. It ended up being in the throttle cables. One had more friction then the other and it was sticking. Then I had fuel spitting out of the carb intake when I replaced the float needles(due to time on the rubber tip) I went back to the old ones and problem solved. Then there was a broken module wire and dead mag and on and on. These engines take a bit of work.Call Lockwood or Mississippi light aircraft.When you find the trouble please pass it to the group.

                                                                   Dick Maddux

                                                                   Kitfox 4-1200

                                                                   Pensacola,Fl



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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Nov 20, 2008 5:16 am Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Paul,



Roger and Dick's advice is all good. Where are you located? Maybe we can help you find a qualified Rotax mechanic in your area.



http://riddletr.googlepages.com/a%26pmechanix

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

paul perry

Joined: 11 Jun 2008
Posts: 36

Posted: Thu Nov 20, 2008 7:45 am Post subject: Re: 912ul Sticking Valves and Carburetor questions.

First, thanks to all who replied and offered suggestions. This is why we feel the intake valves are sticking. We ran the engine for 1-2 min (very rough), then felt the exhaust on each cylinder and found cyl #2 was completly cold. We took off  the rocker cover and by exerting force with palm of hand we could feel the slightest movement on the exhaust valve, but not on the intake valve. Even with a little leverage on the retainer washer with a flat screwdriver we could move the spring slightly but the valve stem did not (on the intake side, the exhaust side was ok). We then replaced the cover and ran engine again for 1-2 min and this time the #1 cyl exhaust was cold the #2 was hot.  That's where we are right now, and my friend the A&P (30yrs exp) realizes his lack of knowledge on this engine so we are proceeding cautiously. The airplane was completed in 2001 and the owner/builder only put 70hrs on it as of this summer when I bought it. He had taken it to the rotax repair center in East Troy, WI in preparation for selling it and they are the facility that did the work incl carb socket replace/overhaul carbs, sync carbs,replaced valve spring retainers/keepers, and whatever R+R of intake manifolds is, as well as replaced the stator. As I said, once the engine warms up, it runs very smoothly, even at 1800 rpm and while I haven't had a compression check since the work done on it at 62hrs at the repair center (they all showed 87/87) it has plenty of power and compression seems good when turning the prop by hand after shutting engine down after having been run to normal temps. I have looked at diagrams of the bing carbs and they show the plastic tubes coming from the carb where I described in my first post, but I haven't been able to find a name/part # etc that might indicate their purpose? Are they some type of vent or overflow? It doesn't seem a good idea to have excess fuel coming out of them as it can fall on the exhaust. I'm located in southeast (rural) Missouri and am not aware of a Rotax service/repair facility in this area, but I'll do some more checking and probably call Lockwood or the place that did the recent work on the engine..Again, thanks for everyone's advice, Paul P.

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Nov 20, 2008 7:55 am Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Paul,



If the tubing you are talking about is what I think it is, they are venting tubes. No fuel should be coming out of them under normal circumstances, but are generally routed to a drip pan of some sort that has a drain tube routed outside of the engine compartment, for fire safety reasons.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Nov 20, 2008 2:44 pm Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Hi Paul,



Fuel doesn't come out of these tubes on normal operations unless the engine vibrates so bad it shakes the heck out of the carb floats or the float arms are not adjusted correctly. I would take the carbs off and check the float arm height. These tubes are vents and if the carbs overflow fuel will leak out. These tubes have to be in the right position. If they are out in the air stream or blocked off it will cause problems like rough running.

If your differential pressure test and a static pressure test are all ok then a valve is not sticking. Mystery oil in the right concentrations won't hurt the engine, but don't mix all the other types fluids. Some people like to use the Mystery oil with 100LL, but we all recommend the 91 unleaded fuel. If you use 100LL alot then use a fuel additive like Decalin to help reduce the lead build up which will work better than Mystery oil. Mystery oil is like Chevy's and Ford's. You like it and use it or you don't like it. I personally don't see a real reason to use it with the Rotax engine.

If it seems to be only when it's cold or low rpms then you may want to double check the enricher circuit (a.k.a. choke).

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

paul perry

Joined: 11 Jun 2008
Posts: 36

Posted: Thu Nov 20, 2008 8:22 pm Post subject: Re: 912ul Sticking Valves and Carburetor questions.

thanks again for the additional info...the reason I added the stabil to the auto fuel is  Lockwood emphasized adding a stabilizer when using auto gas in their intro to rotax engines video. Is there a better stabilizer than the Stabil brand?  Also, another question for Roger...is it possible that if the intake valve is sticking, could it  cause "back pressure" to the carb causing fuel to back up through the vent tube?..just a thought.Again today, after running the engine (rough) for 3-4 minutes..moving throttle in and out some keeping rpm's between 2000 and 3000...it smoothed out and when temps came up to the normal range a mag check was normal...power felt normal in  take off, climb, cruise..only had time for about 30 minutes of flight, but no problems and after shutting down engine the compression felt very firm on all blades turning by hand...Again, thanks to you all...I'll keep you informed as I work thru this, Paul P.

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Nov 20, 2008 8:32 pm Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Hi Paul,

Using Stabil is fine, I just advise against mixing different types of fluids. I still think it is a carb problem. There are a couple of fuel stabilizers on the market. If you fly often enough there is no need for a fuel stabilizer. 91 octane shouldn't set in your plane or storage for more than approximately 4 weeks. 100LL is more stable for the long haul, but you pay the price in leading. If it was a valve it would be a problem all the time and not just start up or only for the first few minutes. It's hard sometimes to diagnose a problem through email or over the phone.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Nov 21, 2008 10:08 am Post subject: 912ul Sticking Valves and Carburetor questions.

If you are having some gas blowing out the throat of the carb it certainly

sounds like a valve sticking open a bit and not completely seating.

I'm with Roger on not leaving gas in y9our plane for extended periods.  Your

engine may be one of the few cases where an hour or so of Ethanol

contaminated fuel may help clean out your engine and allow the valves to

clean up and function properly.  

Noel Loveys

AME Intern, RPP

Kitfox III-A, 912 being installed.

Ivo IFA, Aerocet 1100 floats



--

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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Gtblu

Joined: 18 Jul 2006
Posts: 37
Location: Australia

Posted: Fri Nov 21, 2008 1:09 pm Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Hi All,

Roger, I was interested in your comment about 91 fuel storage issues after 1 month. What actually happens to it in terms of breakdown, and what will that do to engine/carby?



regards

Geoff Bell

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Fri Nov 21, 2008 8:53 pm Post subject: Re: 912ul Sticking Valves and Carburetor questions.

Hi Geoff,



They teach this in the Rotax classes. It evaporates its additives and looses some of its octane rating the longer it sits. Keeping a tight lid on the fuel container only slightly helps. As much as I dislike 100LL it is a more stable fuel. 100LL is made with tighter controls than 91 octane and 100LL never comes in contact with other fuels like 91 octane might during its shipping to the final user. Using really old fuel in a high performance high compression engine may cause detonation and if left sitting in your carb / tank all winter it will evaporate and leave a film which reduces the orifice sizes in the jets. In the old days this happened much faster and a jet could get clogged up. Now days our fuel is a little more stable, but it still happens. The smaller the engine jets like a Honda 3 hp engine the jets orifices are small and letting the fuel set all winter may cause these jets to plug up. How do I know because I was an Mfg. of dive compressors (www.airlinebyjsink.com) (new owner) that used Honda 3-4 hp engines and someone was always calling me in the spring time and wanted to know why their engine didn't run right.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

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