I have checked all of the lines and they hold pressure.... Could it be an air leak at the front bearing? The fuel tank pickup seems to be working normal and moves as should when inverted, etc... Yesterday, I did a sharp turn and the engine sputtered but kept running when I backed off the throttle.... Then I did a loop and the engine quit... next flight I did another loop and the engine sputtered again but kept running... Tryed it again in the next flight and the engine quit in a tight loop.. This has never happen with this engine before so I am baffled.... it is an Enya 60 two stroke...each flight I added a few clicks of rich and it is smoking normal... Held the airplane straight up each time before take off and it takes full throttle with no problem... seems to run good held straight up and during the flight except as noted....

A cold plug will agitate this situation.

You must have an air leak somewhere that the engine is not drawing fuel well.

WBye, I have added some comments to my post.... What do you think?

I just took the fuel tank out of the airplane and found an air leak in the metal tubing of the pressure line from the muffler... Would a leak in the metal tubing inside the fuel tank cause the sputtering while inverted.... I ask because the end of the tubing is open to the top of the tank so that would be an opening also unless the leak which is located in the middle of the tank where the metal tube bends up would be in the fuel most of the time except in when half full and / or inverted... thanks for any info on this problem....

Richard,


Is your fuel tank mounted so its center-line (not nipple/outlet/pipe) is at the exact same level as the carburettor's spray-bar, with the model in level flight attitude?

If it is, the engine will get the same mixture when maneuvering level and inverted.

If not, there's your problem.
Most ARF models will not have the fuel tank/engine combo properly set up... It is up to you to side-mount the engine to get these items properly leveled.

...Do these guys ever try flying the models they manufacture?


Also, make sure the tank is fully isolated from any and all airframe parts, using 1/4"+ latex rubber foam,to make sure no fuel-frothing affects your engine.
That includes the fuel outlets not touching anything solid.

When you checked your tank did the clunk double back and was forward in the tank? A leak inside the tank on pressure side is a problem when it puts bubbles in fuel causing lean runs .

The tanks was mounted center line and was in a model for the past two years without any problem... I did have two hard landings that bent the gear completly flat recently ..... The first thing I checked was the clunk after the hard landings and it had not moved forwarded and was in the proper location.... Since I did find an air leak in the metal tubing on the pressure side that makes me feel confident that was likely the problem.. I have replaced everthing and a new tank with new fittings.... We will find out Monday.... Thanks for the help...

The hole in the line may be causing foaming? Or something else is causing foaming?