HW50

Hello,

I have problems with my engine. In every flight, after 2 to 3 minutes, the engine fluctuates in rpm and eventually stops. I have tried to ease the throttle off a bit when the problem arises, but it stops anyway. This happens even in level flight. The plane/engine has about 30 flights since new, and the problem started after 8 flights or so.

I adjust the main needle with the nose of the plane approx 60 degrees up. Even on the ground I have a feeling that the engine is fluctuating a little bit in rpm at full throttle. If I open the needle more I can hear the engine starting to run rich.

Normally I do not have problems getting my engines to run right, but this one will not cooperate.

The setup:
ARC Cessna. This airplane has the tank in line with the engine.
Pressure feed from the muffler.
Prop: 13x8 and 14x8.
Fuel: 10% and 15% nitro - only a few months old.

I have tried:
Adjusting both carb needles a little at a time both ways.
Modified tank mount to reduce vibration. Tank is supported in foam with rubber bands.
Dismantled tank to check if everything was ok – could not find anything wrong.
Replaced all fuel lines.
Checked valve clearances – ok.
Replaced plug from OS F to same.
Tried to run without muffler pressure. This required opening of the main needle and closing of the idle needle, but did not solve the problem.
Dismantled carb assembly searching for fragments – it was clean.
Returned to factory setting per the instructions, and adjusted the settings to the best of my ability. Main needle had to be turned in a little more than ½ turn to give good rpm on the ground. Idle needle was ok.
Tried both kinds of fuel and both sizes of prop.

Still when I fly the plane, after few minutes it quits. When it does the tank is approx. 2/3 full. I suspected foaming, therefore I ran the engine on the ground with the improved tank mount and the wing off. The movement of the fuel in the tank seemed normal and not excessive.

Several other members of my club has the same plane and engine, and no problems. I use the same type of fuel line as the other club members (standard).

Compression and power is good. Could this be something with the engine? I do not want to dismantle it if I don't have to.

Can anyone please suggest something else to try?

Thanks,
Helge.

Bax

My Feedback: (11)

If you mount the engine on a test stand and run it, how does it run? It does sound like a fuel system difficulty...possibly air is being agitated into the fuel that's in the tank, which will cause erratic running.

HW50

Thanks for the reply,

I was also thinking of a fuel supply problem. However it was so strange that the engine behaved in exactly the same manner after giving the tank a much softer mount.

I will follow your suggestion so that I can monitor the fuel supply while running the engine from full to empty tank.

Helge.