I have a US 41 engine installed inverted (spark plug facing down) on a 1/4 scale super Decathlon plane. My problem is that whenever I try to prime the engine, the spark plug gets wet and and no spark is produced until I remove it and clean it.

Is there an easier way to prime the engine other than putting a finger on the carb or aplying fuel on the intake? maybe something like the small plastic priming bulbs that some engines have?

Has anybody else used this engine on an inverted position?

Any comments and suggestions will be appreciated. Thanks.

You could invert the plane and prime it or use a starter and not prime it.

I tried a Sullivan high torque starter (about 350lb-in, the second strongest from Sullivan not the one with two handles) but it couldn´t turn the prop. Maybe I need to install a spiner because it doesn´t have one.

What kind of starter have you used?

I use a Hobbico 180 with a Miller 4 to 1 belt reduction on it with a 275 amp garden tractor battery. The battery is $20.78 at NAPA stores.

A standard Sullivan starter will do the job if you have a seriously big auto/truck battery to power it.

It sounds as though your carb may be malfunctioning if the engine fills up with so much gas that it hydraulically locks the engine up. Am I reading your post correctly?

The engine doesn't hydraulically locks up, what happens is just that the spark plug gets wet and I guess that prevent it from making the spark. After removing and cleaning the spark plug, the engine usually starts with not much problem.

The difficult part is to know how much to prime the engine without having this problem. How to close the carb. air intake and turn the prop without help from another person?. I had a Zenoah mounted on an UltraStick and I had absolutely no problems with it, I just turned on the choke on the carb. turn the prop and when it wanted to start, I just put the choke in the normal position and it would start very, very easily. This is not being the case with this US engine.

Is there a way to install a choke on the carb similar to the ones used on Zenoahs?

Thanks.

Sorry for the misunderstanding. I get it now.

My Quadra Q-35 was sensitive to flooding (a not too distant relative of the USE 41cc engine). I always suspected the spark wasn't all that strong. However, I did get used to the drill eventually and was quite successful at handstarting the engine.

Check the spark plug gap and the magneto gap. Either/both will cause weak spark if not spot-on. Good luck.

I agree with you. Do you know what the those gaps should be?

Thanks.

No, not off the top of my head, I don't.

Coil clearance is .010 . Sparkplug is .025.

Thank you very much, I will check it.