I have a gas engine that is new off a gas scooter and it seems to knock or ping,is this what everyone is refering to as detonation ?Can I just shim the head and lower the compresion?I have never had this problem on any of my airplanes but then again I didn't get them from china either.
ps I took it apart and found nothing wrong with crank and bearings I even tried changing the carb and running it so rich it would barely run and still pings ,could this be timing ?there is no way to adjust timing .

Darin

sounds like predetonation just as on a car.Since you can't adjust the timing try a hotter plug and higher octane fuel.

You actually want a colder plug to stop detonation. Make sure you are getting an adquate supply of fuel and you are not running the engine lean.

It's rather unusual for a 2 cycle gas engine to detonate unless the coil is bad and it is firing completely wrong.

Are you sure it's detonating?

Two cycle gas engines when not loaded down will make a cackling sound and some times break into what's called four cycle if they are rich enough. This is especially evident when decelerating.

Go back and peak out the top end and then richen it slightly. Then adjust your low end for smoothest running and lowest speed. then check your transition back to high speed. If it just quits, the you have to richen up the low end some to where it will speed up without quitting.

Jim

Two-strokes will detonate if the timing is too far advanced, compression ratio too high, excessive carbon deposits in the combustion chamber, spark plug heat range is too hot, octane of the gas too low, if the cylinder temperature gets too high, or if the load is too high. Premix oil in the gas also lowers the effective octane of the mixture.