[450pa]

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!

 

[hoser]

If you put the lid on without re-jetting, then yes it will run like crap. There is a huge difference with lid on vs lid off. You can read the jetting sticky in the engine forum to help you get it jetted and tuned properly, but personally if it ran good with out the lid I would just pull the lid off and run it like that.

 

[450pa]

Ya, I have no problem running it with the lid off. The issue is it backfires like crazy with the lid off. I was told then means it’s lean and it’s not good to run like that for a period of time