Little 100cc 4 stroke atv. Don't remember brand off hand. Getting good spark, getting fuel - jets clean. Cupping carb, I get fuel. It will only pop ONCE, at random. Never anything other than one pop. I can turn it over 10-20 times, and i'll always get one pop and nothing.

I bought a feeler guage, so that is my next check. I was thinking maybe the timing is off? If timing and valves look good, would the next step be removing the engine and checking rings?

This has become a new obsession, err, hobby of mine. This is my 5th chinese wheeler, and really has me stumped.

 

After checking valve timing, if I was you I'd do a compression check before taking the motor out.

 

Did you replace the plug?

 

I had the same thing happening with mine... after having it for like 3 days
I tore apart and checked a whole bunch of things and still nothing. then someone suggested simply changing the spark plug even though the one that was in it was brand new (came with the machine) and had a nice blue arc.

After 3 weeks of non running frustration, I was pretty sure something that simple wouldn't help a dang thing, I mean really the plug in it sparked fine! Guess what? Changed to a good NGK plug and it started right up! Haven't had any trouble with it since. So yeah, if you haven't done that yet, even if the plug in it seems to throw a good spark, I'd change it.

 

I would change the spark plug then pour around a teaspoon full of gas into the spark plug hole, put spark plug back in and try to start it up. If it doesn't try to start up or act like it wants to start at all then I would check the valve clearances. If clearances are right then I would do a compression test. If compression is good then check timing.

 

Yeah that's how it goes sometimes. The spark plug that was in it probably was not grounding properly when it was in the spark plug hole but was sparking great when grounded outside of the cylinder.