Hi, i have a 2005 kfx 400, it has a pro circuit t4, no air lid, but no jet kit on it. It starts backfiring immediately even when cold, and after it warms up, it bogs down when you hit the throttle. What can i do? Any help would be great

 

You need bigger jets! Main definitely, possibly a bigger pilot. You are moving more air with the exhaust and no lid, so now you have to add fuel back in.

 

Thanks a lot! any brands / sizes that are recommended?

 

thanks a lot!! and brands / jet sizes recommended?

 

For simplicity, stick with your carbs manufacturers parts. They all seem to have different numbering systems. If your machine was stock, then you are close already and only need to go up a few jets at most.