my '02 (essentially stock) wr 426 backfires when i use the engine compression to slow down. am i too rich, too lean, something else?

i'm currently running a 168 main, 40 pilot, clip in position #3 (7,000' altitude). i haven't adjusted the air screw from its stock position.

the backfiring occurs more when the engine isn't completely hot but never really goes away.

any thoughts?

my 02 did the same thing until i leaned it out curently i am runnung 155 main,needle on #3 i may try position #2 later.I also have b-k mod and kouba t i fiddle with ocasionally to get motor to run at peak per altitude.been riding at 1500-3500 feet lately this will drop for the winter months to sea level.hope this helps :)


take a look at my jetting and see what you think.


The ACV (air cut valve) mod should help the backfiring problem. It only takes a few minutes to do and if you want you can "undo" the mod. Here is the post on how to do it. Just reverse the diaphragm.

Also it looks like you are probably too rich. My jetting setup is in my signiture. Hope this helps.

I am thinking about a Canadian wr450. I know they don't have a throttle stop or grey wire. But,looking at the carb stuff I think there may be more differences. Do the Canadians have an air cut valve? Thanks, Mark

I think the Canadian WR426 has the ACV, I'm not sure if the 03 WR450 will though. My guess is it probably will.

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