[marcstryd]

I just rebuilt the top end on my 400 ex. Was burning lots of oil. It had white brothers exaust and k&N air filter, 38 pilot and 160 main jet. I bored the bike .20 over and put in a high comp 11.1 wiseco piston. I also put in stage 2 hotcams. Now, I already changed my main jet to a 172 which seems alot better. Is it recommended for me to increase my pilot jet as well? seems like it might be a little lean at lower rpms, seems to pop a little on decel. thanks

 

[tumtumsback]

160 main is big to begin with. I think stock is 148. It might be popping on decel because the main is too big, and the popping is from unburned gas. Not exactly sure, but try putting 160 back in and see if it stops?

 

[Here 2 help]

Try turning the fuel screw out about 1/2 turn and see if that helps. Popping on deceleration is normal with a reduced restriction exhaust. It won't hurt anything, it's just annoying.

 

[trx2fiveO]

Most likely you're going to end up in the 178 range? I would set the fuel screw to 2 3/4 turns out from lightly seated and install a 42 pilot jet. Running a proper plug chop will be your best helper in determining what main to use? Your altitude and outside temp will also play a huge factor.