If I put a K&N on a stock z400 with the air box lid on will I have to re-jet? Will I have to re-jet with air box lid off?

 

Hello.
You do not have to re-jet if you leave the cover on. You will have to rejet with the cover off. Your stock main is a 130 (Mikuni). I would go to a 132~135(mikuni) main. You should not have to mess with the needle or low side jets.

 

Thanks man