Backfiring flames not starting

I've got a 2000 drz400. The bike sat for 3-4 years before I bought it. The jets were clogged, so I rebuilt the carb, cleaned the gas tank, changed all the rubber, and the bike ran great. I used the bike for commuting to work daily, never had a problem. Then, I was heading home after an 8 hour shift and the bike lurched forward a few times, lost all acceleration, and backfired severely. There were flames out of the exhaust. Since then, I have re cleaned the carb, but the bike won't run. It will whine the starter, but never catch. If I spray carb cleaner into the intake it stumbles for a second, then dies. I checked the carb, cam chain timing, and compression. i also replaced the spark plug. Any thoughts?? I feel like its a fuel problem. I pulled the plug today and it barely smells like gas.

is fuel flowing out of the petcock?  Does it have the vacuum petcock or a manual one?

It has the vacuum pulse petcock. I took apart the petcock and cleaned it well. Gas flows out of the main, but not the smaller.

"smaller"? vacuum line hooked up to carb and petcock?

Yes. The smaller pipe coming off the petcock. I'm not sure if the petcock is working properly.

2 things spring to mind...

 

You have checked the compression - how?

Have you done a leak down test or a proper compression test or does it just feel like there is compression there?

 

Have you checked the valve clearances to see if one is now more open, or stuck open.

Has it got spark..??

Would the backfiring indicate the presence of Spark ........ M8 ?

Has it got spark..??

It's got spark. And, I have done a proper compression test. I have not checked the valves. I have the feeling it's a fuel problem. The plug looks like its running very lean.

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