boyesen goodie

3 replies to this topic
  • #55 2002 WR426f

Posted March 20, 2005 - 09:58 AM


My ride is an 02 wr426 (canadian) that has mods. powerbomb head pipe, powercore 4 tail pipe, removed air box cover, uni filter, racetech front and rear boingers, yz tank, shrouds, blah blah blah. Most notably, when I got it, it was hard to start, hard to keep running and was popping all over the place. Didn't take me long to figure out that it was as lean as it could be. With help from Chris at FMF on jetting, I finally got it to start, run and perform well with the exception of just off idle. When I blip the throttle it usually picks up well but if I goose it too quickly it will stumble and then go. Where I ride we do a lot of technical trasition from climbing to descending (deep water bars). Good throttle control being the key to having a good day up there. I have surmised that the measured blast that the accelerator pump gives when the throttle is rolled on is not enough to go with the other mods. Boyesen now has an aftermarket diaphragm cover that is supposed to work very well. Is anyone out there using it yet and if so does it work well on a wr426 :)

  • Seabass

Posted March 20, 2005 - 04:39 PM


Everyone on this board seems to believe in changing the leak jet. I've only seen posts on the wr 450 and the stock lj is 100. People are changing it to a 40. I put the Factory R&D accelerator pump cover and have only ridden it around the neighborhood so I can't really comment on how well it works just yet

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  • Tyler426

Posted March 20, 2005 - 09:12 PM


In the May Transworld they tested it and loved it, but 90 bucks seems alot for a little piece of aluminum. Seems like if you knew what you were doing you could modify the stock one and get simular results, but you may screw it up in the prosess.

  • Plusdome

Posted March 23, 2005 - 07:23 PM


I've got the P-38 cover on mine and since I fixed the problem in the thread you posted on yesterday(It was a clogged pilot jet/oxidation in carb) I have none of the down low hesitation everyone speaks of. This may be a fluke as I have yet to give it a through flogging but i will let you know. Many people on this forum speak pretty highly of the P-38.
Here are some links......for the P-38
Factory R&D
Thumper FAQ
In the new transworld they tested and spoke very highly of the boyesen accelerator cover, but who knows??


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