I just rebuilt my bike i put a wiseco high comp. piston with 10 over rigns and filled them down to fit just right but when i started it up it was running like crap. Im having a problem when i give it gas nice and easy as soon as i get to 3/4 and more it start back firing but low and mid range is perfect but when u open it up slow it pops. I checked the plug it was kind of rich. DO u think if i adjust the pj it will get rid of that. by the way i have a 160 main jet. Funny thing is that before i rebuilt the bike it was running fine. I need help guys let me know so i can get this bike running right thanks

 

is the jetting the same as it was before the rebuild? Just going up in bore diameter... especially such a small amount... shouldnt warrent rasing the jetting. What other mods do you have?

 

Check your timing marks, sounds like you might be one tooth off. I did a 300ex and it popped at half throttle and up. It was cam to crank timing.

 

If the other suggestions don't work, you might also look at the main jet. It controls jetting from 3/4 to full throttle.

Backfiring is a rich condition, popping is a lean condition.
Adjust jetting accordingly.[img]i/expressions/face-icon-small-wink.gif[/img]

 

With the 440 Kit it's very hard to get the carb jetted right, infact its a pain in the ***, look into a new carb made for the 440 kit. You might want to check the notch of the needle and also dont use those stupid manuals on what jet you should use test them out and find the right one those things are not accurate to every condition,

 

Thats bull... took me an afternoon to get mine dialed in perfectly... Nice brown plug [img]i/expressions/face-icon-small-smile.gif[/img] Now... im not saying that an aftermarket carb wont make better performance... but... Most aftermarket carbs... especially the FCR series from kehin are a PITA to tune correctly... And using metering rods, like the lectron, and the edelbrock, are never dead on perfect...