Engine Running Rough

Here's the situation...I have a 2001 YZ426F and it cranks perfectly 1st or 2nd kick every time. The bike was running fine the other day and then started running rough. Where I'm all confused is the bike will crank fine and idle fine but will not run smooth when you give the bike more throttle. It starts missing and popping and cracking, sometimes shooting a flame out the pipe. And when you pull the choke out it runs smoother and when you throttle the bike up it is smoother, but still pops and cracks. And when you kill the bike you can hear it make a "boomp" sound (best way I could describe it lol). Almost sounds like it may be a flame blowing out. I pulled the carb off and cleaned the jets and what I thought was all the ports. Has anybody else had this problem? Any suggestions on what else to do? I'd rather work on things my self, but I'm almost to the point of taking it to a shop so any help is greatly appreciated.


Start by checking the float bowl plug for dirt or water, then the vacuum release plate on the slide and then the cam timing.

+1 on the cam timing.

carb to head boot! they get cracked up, and air comes in after the mixture is made, causing too much air and a really lean mixutre. if you put the choke on and it runs ok check that for sure. spray starting fluid on the carb boot and if it idles higher than theres your problem

I'll look into these. Thanks for the help guys. I'll post when I figure out the problem.

Figured it out guys...CDI went out. Bought one on eBay fixed it up good as new. Thanks for all the input guys.

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