03 YZ250F, dies and is hard to start..

Ok like the title says... Im at my wits end with this bike. It has a new topend, overhauled the carb. checked and set float lvl. Im pretty sure the jetting is spot on. I can be riding along and it will just die. doesnt stall like a flameout or anything. It just dies kinda like it runs out of fuel. Sometimes it will fire right back up and sometimes you have to kick the crap out of it. Its been a little while since I was in the carb, but I think the jetting is 178 main and 45 pilot, we are around 1500 feet here.

This is very unlikely but I ha a breather on my tank that for some reason was not working and would not allow my tank to breath and caused my bike to die multiple times on a fairly short ride, as soon as I took it off ran perfectly. Idk if that will help, but that starved my bike of gas, goodluck.

Any chance you've checked to see if your plug is fouled?

no plug is fine, and you know I thought about the gas cap breather after I posted this thread. My old KTM 520 use to do the same thing. this bike has an aftermarket cap on it because I bought an oversized tank for it. next time it happens Ill pull the cap and see what happens. Thanks.

Any luck?

but I think the jetting is 178 main and 45 pilot, we are around 1500 feet here.

well there is your problem!!!

do you know what the actual jetting is or dont you?

and a 45 PJ is WAY too fat. 42 at most and probably needs a 40.

your jetting is all wrong for OK unless you are racing in the snow.

what fuel are you using?

however, the symptoms suggest either a plugged breather like you said or a plugged carb vent tube.

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