So I bought this 04 450r. It ran awesome. Noticed the air box lid was gone so I bought one. Still ran great. The hmf slip on fell off while riding as it was clamped on w tin. So I bought a mega clamp and made sure it wouldn’t come off. My last ride it started to sputter and surge after 1/2 throttle. I cleaned the carb and it still has the same issue. I then found out w o the airbox kid it has no issues but it back fires a lot while decelerating. I put a new plug in and the one that came out was black. It has a 180 MJ and a 52 pilot. If I’m correct. I’m just looking to get it running great w o all the backfiring. Thanks for any help!