Hi everyone, I am new to the sport and new to this forum.
I started flying a few weeks ago with a Lan Yu trainer powered by a .40 engine.
I would like to know if too big of a prop size could cause the engine to cut out at lower rpm?
I am currently using a 10-8 prop. Is that too big for this engine?
It is an old engine (about 20 years old) but it seems to work just fine until I ease off on the throttle.
My instructor has set the engine's fuel mix but it still dies on me every other flight leaving me with a hair raising powerless landing.

Thanks,
Ray

G'day Ray,
Try a 10x6, I dunno what engine you have, you didn't state, but a 10x6 is a good starting point for a 40.
Also, it so like your low speed mixture is not right, try the pinch test, to check if it is rich or lean, or get your instructor to do it, & reset you low speed mixture.

Thanks for the help Alan.
It's an old Italian motor, a tigre I think.
I will put on a 10X6 prop and see if that helps.
Pinch test? How does that work?
Very green here, still got a lot to learn.

G'day Mate,
Ask your instructor, he should be able to help.
If not, do this: run engine up to full speed, on the ground, to get it hot, then take it to idle, stand behind engine, & squeeze off the fuel line to the carby with your thumb & forefinger, beware of the PROP, it will cut you, listen to the engine, if it speeds up a lot, before slowing down & stopping, it is too RICH, lean the idle mixture 1/8th of a turn, this is where the instructor will help.
If it just dies without speeding up it is too lean, richen mixture.
You need it to speed up a small amount, maybe 50 revs or so, before it dies, then it is perfect.
Your high speed mixture should be rich enough so that at full power, when the nose of the plane is held up at about 90 degrees, it should pick up some revs, if it doesn't or it dies, it is too LEAN, richen high speed needle, until it does.
Then the mixtures are set, leave them alone after that. The biggest problem I see at flying fields is when people continually tweak their needle valves, & have no idea what a properly tuned engine should sound like.
A couple of weeks ago a new flyer turned up at our field, he said he tuned his engine to perfection, he is a retired car mechanic, when we got it running, it was 1/2 turn too lean, that is a lot in our engines, it was retuned & has not had to touch it since.

Thanks for the info, much appreciated.