hey guys,

i just got a new exhaust on the 426er and it is starting to backfire when ever i let off the throttle. it never did this with the stock exhaust. so i am wondering if it needs to be re- jetted or what? thanks for your help!

I took my 426 to get a full service. One of the p

roblems i hade was backfire when i let of the gas. What they told me they where going to change the main jet one size bigger. I have the R-4 from white Bros. I also called white bros and they told me to also change the main jet one size bigger.

The usual scoop is a more open pipe requires richer jetting. Backfiring (or more specifically popping) is a lean indication. Go richer.


Go with a 168 main. You probably wont have to mess with the pilot or needle unless you start messing with something else.

My 2000 backfired horribly.

Check for air leak in the exhaust and clean the hell out of the carb. This may work for ya.

I did the BK mod, went to a 168 main and a 48 pilot w/ 1 1/2 out on the air screw and whamo!! Power that eats a CR450 and no more backfire!!

just my experience.

-jp :)

Good advice from above posts. As a starting point, you might want to try enrichening the fuel screw a little. From my personal experience in jetting the 426, some popping on decel is desirable. Why? Because you get sharp throttle response when you blip the throttle at low RPM. The aim is to get a muffled pop on decel. It shouldn't be loud or a series of loud pops. Aim for one semi-loud pop followed by one muffled pop. If you can get a kind of "crackling" sound on decel, that is even better. The bottom line is throttle response.

I had the same problem. I noticed that if I opened the throttle just a little while decelerating, the popping went away. I backed the the fuel screw out just to 2 to 2 1/4 turns out, and the problem is pretty much gone. I also had junk in the pilot jet which caused it to not idle. Once I cleaned that, the bike ran great. You can get a short stubby screw driver at the auto parts store that will fit right into the float bowl counter bore where the fuel screw is. I think I paid under $6 for a package of 3. this makes life much easier to adjust that fuel screw!

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