So here I am back with the same problem. After having a 100h check a few weeks ago we discovered that the reason for my rpm-surge (+-200 rpm) was dirty carburators. After having everything done i flew home (1 hour flight from maintenance) and the engine felt like an electric engine. Very smooth.
In the last few weeks I had a total flight time of 5 hours, always flights 20-30 min.
Yesterday I took the Gyro for a 1,5 hours flight and after appr. 1 hour the engine surges started again. In 2 seconds from 4900 rpm up to 5200 and back again. The whole rest of the flight (20 min). I decided to fly back to my maintenance guy.
Has anybody an idea what reason it could be? At the last 100 h check everything was done very thoroughly and they did spend many hours to find the reason.
The new idea is that maybe the fuel-line after the filters which goes to the 914 might be in a bad condition and thats why the carburators got dirty.
With an engine like this I don't want to fly anymore, I had my forced landing with the Gyro already this year!
You have to find the source of the contamination, if you suspect the fuel supply hoses are breaking down they will all need to be replaced with hose that can tolerate ethanol/avgas/mogas.
And then the whole system will need to be cleaned again.
If carbs were dirty and the problem you may have cleaned the carbs, but still have debris floating to the carbs. Common causes are fuel hose was just changed and it wasn't done sterile enough, fuel hose clamps too tight and the hose has been cut inside and debris floating downstream, old hoses starting to breakdown.
Roger Lee LSRM-A & Rotax Instructor & Rotax IRC Tucson, AZ Ryan Airfield (KRYN) 520-349-7056 Cell
Check all the o rings in the carb. If they leak then the carb will not hold pressure or it will suck air from the wrong place. This may cause the float bowls to empty and then refill causing the surge. You may also want to check the screens on the fuel pumps. If they are restricted it can cause the same issue. I would also check the vacuum lines that connect to the pressure regulator. If they are cracked or leaking it will have a similar effect.
It seems my mechanic has found the problem. It has been a plug attached at the turbo. Which one exactly I dont know yet. The gyro is still at mechanic and I spoke only to the secretary in the office. Hope I can pic it up these days.
The fuel lines are also made all new, after 5 years they have to be replaced anyway....
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