I recently installed a venerable and reliable 52fs in a new model and the first flight was fantastic. Loads of power and supremely reliable. The next and subsequent flights were horrible, loads of dead sticks and leaning out in flight even though the needle was set fine on the ground (though now to 1 turn out, usually a bit on the lean side for this motah). I'm using Duraglo 5% and an 11x7 prop.

I attached some fuel tube to the carby nipple, screwed the needle valve fully home and blocked the carby mouth with a spare digit and blew. No air leaks. Tried the same with the needle a turn out and leaking air. When running, waggling the end of the needle valve side to side doesn't change tune.

Is it likely that the needle valve o ring has gone letting air sneak past and making the whole caboosh a bit lean and hence gutless?

Milesgoff,

If wiggling the needle doesn't cause any changes, then it's not likely the needle's leaking air through the o-ring.

If the engine's leaning in flight, we'd start to suspect vibration-induced fuel foaming. That will cause the engine to go lean in the air and quit.

If the engine will run fine all day on the ground, but not in the air, it's not the engine, but the fact that the model's vibration mode is changing when it gets off the ground.

Also look for fuel lines moving about. That can cause erratic fuel delivery.

Bill
Thanks for your response.

I agree the needle valve 'wiggle test' is pretty inconclusive, however....

I replaced the o ring with a non OS one (wrong size, wrong make, only one I had) and tried to improve seal with PTFE tape. No point PTFE doesn't seem to like glow fuel. So I tried the old timers trick of a few winds of cotton thread to 'bulk out' the o ring and improve the seal. This helped increase ground RPM by 1k to 11.5k, I've yet to flight test it though.

In case you're wondering, I do have the proper o rings on order!!!!

I'll report back when I've had a chance to flight test.