Yz 125 problem

So if I'm getting spark, air, and fuel, and I've got plenty of compression, why is my bike not starting?

you need to be able to maintain pressure in the crankcase to help draw fuel up through the transfer ports.

Did you do something to it recently like mess with the float height? Sitting for awhile? Choke working? Kicking it only or have yea been able to try push start it?

Fuel could be old & stale. Or jetted so poorly that it's flooding itself out.

Or the spark could be incorrectly timed, with a sheared flywheel key.

try lean the bike over on the flywheel side untill fuel comes out the overflow then give it a few kicks 

Fuel could be old & stale. Or jetted so poorly that it's flooding itself out.

Or the spark could be incorrectly timed, with a sheared flywheel key.

These would be my starting points. Spark is no good at the wrong time. Check under ignition cover and see if timing plate has moved or woodruff key sheared. Or moisture and crud on pickup that will let you have a spark but not good enough to fire. Then drain old fuel and put fresh fuel in. These are the easy ones.

Was it running good and then just quit? Or have you ever seen it running?

The bike was running like a champ for about 6 hours then all of a sudden died and hasn't started since.

Just because you have spark from the plug when it's outside the cylinder, does not mean you have spark inside the cylinder under compression. Have you tried changing your plug?

Is the spark blue or yellow? Pour a little fuel in the  cylinder and see  if it starts.

I've tried 2 different plugs

Disconnect the kill switch and try to start it.

Had my '06 running fine in the woods,when we were done for the day I tried starting it to get back to the truck...would not start for anything! Thought I was out of fuel,but came to find out the next day I was not...still not starting....everything seemed to check out from a clean carb,fuel,compression,spark... Turns out the fuel line coming from the Gas tank was split...just not getting enough fuel.

try lean the bike over on the flywheel side untill fuel comes out the overflow then give it a few kicks

I tried it l, still no luck

I tried it l, still no luck

hmm so it was running well then died.. how did it die sure u got good compression

Have you tried the killswitch trick?

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