Bog then died then no start

Yesterday was riding for 10min then came out of a corner then it bog down then just died and would not start back up. I pulled the plug it was alittle black and check spark and it was good. It seem like it kicks the same with and without the plug in. But has some compression, maybe the decomp is sticking?

CAN YOU SAY ROACH.....if it it kicks the same with or with out the plug in, you got a problem, whether the piston went, timingchain jumped or a valve is not sealing, you are more than likely going to start the teardown process....Inspect everything as you go....Check cam timing before you start tearing everything off, to rule out the timing chain jumping...

Right I know but it feels like something is there still and when kicking It, it will backfire in the exhaust

Check cam timing..... Poping out the exhaust usually means jumped time.... does it consistantly pop out the exhaust?

Not much info in your first post.

Like is it a WR or a YZ?

Maybe even a model year would help.

And any mods you have done to it would be a huge help.

No just once and awhile from kicking it might just take it to a shop I'll cheak the basic stuff

It's a 2005yz250f with just a carbon pro pipes

It's in time, just seems low on compression, i just put new rings and a piston in her

Also I just rebuilt te whole engine, crank rod and piston, and after I put everything together there was no comprission at all then after a few kick the compression came back or on then it started up put a new plug in it?

yup new everything

found the problem seem like the valve failed where the keeper hold the valve onto the retainer.

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