Needle should most likely be in the middle clip position. Have you ever taken the carb apart & cleaned it out completely?? If not then I'd suspect the jets are clogged up & in turn it leaned the engine out bad.

 

Yes i had the carb apart and cleaned it.

Thanks for your help
tutiii

 

You said the hole was under the spark plug I beleive and if so the timing maybe advanced too much (which would add to the problem of leaning by outside temp and lack of fuel. Is the top part of the piston pock marked with a bunch of little dimples besides the main burn area?

One other thing, if you used fuel that had over 10% ethanol, that would have added to a lean condition.

 

yeah, that is what it looked like. the plug was gray and dry.
this quad ran fine, so main suspect is the oil injection when bad.

i should be able to test that by pumping throttle and see if oil is
coming out the end of the line, correct?

thank
tut

 

If the tope of the piston is pock marked, that is a sure sign of detonation.

Detonation is mainly caused by a lean mixture, advanced timing, and too hot of heat range in the spark plug.

If it were me, I'd fix the piston and put all carb and timing settings back to stock.
Then, make one & only one performance change at a time. Write every step and setting down so that if a change makes the performance worse, you;ll know where you were.

You can't tune a poorly running engine into a killer race engine. It has to be running right in the first place to give you a good base to start from.

 

Thanks,
i never changed anything, this quad was all stock.
that is why i think it is the oil injection.

thanks again
tut

 

oild injection i think would seize the engine before it would burn a whole in the pistion right under teh spark plug and you said it was smoking so it has oil. it sounds like a timing issue i have the 2 strokes in my race car and when you play with the timing it will burn right under the plug and melt the plug tips and clean off the plug but thats with methanol so the plug stuff will be diff. but burning under the plug seams like the cdi is going your stator /magneto is miss aligned. i would first think it is the cdi those can go out of nowere and blow engines.

 

if it was due to lack of oil generally you get 4 equally spaced score marks down the side of the piston corners and cylinder, not a hole in the top. Sounds like you have a lean condition. If the atv has run fine in the past and you didn't change anything than I would suspect you have an air leak. I would first look at the carb to cylinder boot for cracks that may allow extra air into the cylinder. If that looks fine I would next start to suspect crankshaft seals. A leakdown test can pick this up. I believe the crankseal behind the drive clutch takes a lot of abuse and can be visually looked at pretty easy.

FYI These are tough well designed motors. I've had my 400L in weather as cold as 5 below zero with stock jetting and not had any problems. I'm not running the heck out of it when it is this cold but 30 deg temps should be no problem with a stock setup.

 

thanks
i'll check for the air leaks. i took a look at the carb yesterday and it was fine
i'll look at the boot today.

thanks
tut