912s Engine Problem Help

[DesertFox4]

Welcome to TeamKitfox Brannan. I also doubt the carb ice just yet and also suggest a close scrutiny of your entire fuel delivery system. With the info. provided it sounds like fuel delivery restriction. If the aircraft is brand new check your fuel filter/filters for contamination from fiberglass from the fuel tanks. Make sure your are flowing enough fuel at the engine to maintain full power for extended periods of time. Your engine will consume between 7 and 8 gallons per hour at full throttle. You should be delivering a good percentage over that for safety. 50% over max fuel usage should not be at all hard to acheive sitting on the ground in any configuration. That is of course with no ram pressure at all from the fuel cap tubes. If not look for any restrictions and that goes for fuel lines that may look normal from the outside. If you are useing the old fuel valve supplied with many of the older model 4 kits I would inspect that real close. The old models used o-rings inside and they are susseptible to damage and blockage of fuel flow.

Good luck and please let all know if you find the problem. Be careful in the meantime.

[DesertFox6]

Welcome aboard Brannan; you can easily tell this group isn't very interested in your problem, huh? What a group! Wouldn't it be nice if our medical service here in the states was this responsive and diligent?

I'm going to cast my ballot with the "fuel restriction camp" in regard to your intermittent power "sag," and I agree with all the data presented here with that cause in mind for checking things out. Before you start selecting wrenches though, I'd like to suggest a simple trick that won't hurt a thing, but will definitely make your entire engine happier in the process if it doesn't cure or at least mitigate your problem while you're checking everything else.

Go buy a quart of Pennzoil 2-Stroke (yes, 2-stroke!) motor oil for air-cooled engines available in the aviation department of your favorite Big-Box store. Thoroughly mix this into about a gallon or two of 100LL (since that's what you're using) and then split it evenly between each wing tank. Doing this just before filling up will obviously allow quicker dispersion of this cracker-jack, fool-proof, engine/carburetor/pilot's-mind-cleaning compound: This is what solved all of my similar power-sagging predicaments on the recommendation of our local ROTAX 912 guru, Steve Beatty of Airscrew Performance here in Glendale, Arizona. I'm willing to bet your early-in-flight fuel-flow drop, resulting in your heartbeat-altering experience, may be caused by carburetor contaminants that break loose early in the high-power-on phase (think needle-jet area here) and then disappear for the rest of the day's flying: Altogether possible and just as maddening.

You might want to do this 2-stroke stuff every 3-4 months or so even if you find a fuel restriction problem elsewhere, as this will nicely polish everything in the engine except the wiring and, as I said, your engine will thank you! (I do and mine DOES! )

Sometimes the simplest factor is the fastest fix; it's pretty easy on the wallet too. Give it a try while you check the items the rest of the gang has suggested and please keep us informed of what you find!

"E.T."

[leptronjohn]

I had what seems to be the same exact same problem 2 years ago, I fought it for a year.
I replaced the carbs nothing, I had the ignition checked, nothing, I checked fuel flow at carbs, nothing. then I pulled a cylinder... I was appalled.. I had been using 100LL for the last 150 hours and had sulfur build up in the heads, pushed up by the pistons. the rings were clogged.. it looked nasty. I wanted to cry, only had 400 hours on engine.. it went off for a top overhaul..
they actually just cleaned the rings and groves, heads, completed valve job, they were sticky... lead, dam
runs good now.. john Oakley
801-821-6175

[Av8r3400]

It is absolutely imparative that when you run 100LL in a 912 you keep your temps up to burn the lead off. Even with a lead scavenger additive. Several comments on this at airventure.

[Dorsal]

So you are saying my high CHTs are a good thing given I primarily burn 100ll.

[Av8r3400]

According to the seminars here at OSH, yes heat and high power settings good, cool low power, bad when running LL.

[Dorsal]

Leptron, out of curiosity were you using Decalin and 25 hour oil changes? I often wonder if these procedures help much or just delay the inevitable. I have seen pics of engines after a steady diet of LL vs Mogas (reminds me of the healthy lung smoking lung pictures). Would like to see pics of an engine after 1000 hours of LL following all the best practices.

[leptronjohn]

dorsal,
I always change oil at 25 hours, the decathlon was discontinued the last 100 hours. I did not feel it was going to be detrimental.. I was wrong.
I think there are others that have suffered the same. the first tail tail was pulling the exhaust, the valve stems were covered with crap. I broke my heart.

[Av8r3400]

What oil were you running, John?

[leptronjohn]

I was and am still running the Honda Simi synthetic oil.. the oil shows no problems at all and was agreed by Lockwood who did a top on the engine.
I have not been able to keep on the site like I should, you guys can contact me at john@leptron.com also.