Yz426 problems

[07658]

I have read a lot on TT but can't find an instance like mine. I recently put new rings on the bike, long story, but I decided to check everything while I was in there and everything was within spec. After I got it all together it ran great then the next day it was like I had a fouled plug or it was out of time, popping and backfiring with a bad bog, idles fine though. After an hour or two it runs great again. A week later and it is screwed up again, this has gone on for quite a while back and forth and I have checked and rechecked the timing gone through several plugs, cleaned carburetor a couple of times and still this stupid problem. This morning I went to go riding and it didn't work, after cleaning the carb one more time it worked, until I got there and it acted up again. Any help would be appreciated and sorry for the long post.

[07658]

Sorry it's an 2001 yz426 f all stock

[grayracer513]

Seen this?

https://www.thumpertalk.com/topic/966405-03-yz450f-stalls-hot-no-spark-help/

[07658]

I wondered if this may be the problem, bout the only place I haven't gone with this bike, another thing though, now I can kick through on occation without decomp lever, basically like my valves are stuck this just happened today for the first time just after I posted, and I was wondering if trying to "ride through the problem" could have done some serious damage? Thanks for the info gray.

[grayracer513]

If carbon builds up near the edge of the valve, it can sometimes hold a valve off its seat enough to reduce the cranking compression quite a bit. Not that unusual, and usually temporary.