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Boyesen Accelerator Pump Cover

By Seabass,
in WR400F/426F/450F

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Seabass

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Has anyone tried the accelerator pump cover that Boyesen makes? I took my '05 WR 450 to have the carb serviced after sucking in some sand and told the mechanic to change the leak jet to a #40 while he had the carb apart. He told me the Boyesen product would work better than changing the leak jet to cure the bad bog I'm getting when I crack the throttle open. Is he high or is he on the right track. He didn't seem to know what a leak jet was when I was talking to him ?

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cruise

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Has anyone tried the accelerator pump cover that Boyesen makes? I took my '05 WR 450 to have the carb serviced after sucking in some sand and told the mechanic to change the leak jet to a #40 while he had the carb apart. He told me the Boyesen product would work better than changing the leak jet to cure the bad bog I'm getting when I crack the throttle open. Is he high or is he on the right track. He didn't seem to know what a leak jet was when I was talking to him ?

I guess you will have to buy one and let us all no if it works ??

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Dan_Lorenze

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I want to look into what makes the Boyesen pump cover work better than the stock cover. I Mean, certainly we can come up with a Mod for it. Is it that the stock cover allows too much volume? Not enough volume? The pump does have an adjustment on it. Back when the BK mod was around we would adjust the squirt duration to limit the initial "flooding" of the carb, the problem was too much gas.

Changing the volume of the stock accelerator pump would be easy if that's the case..

Any thoughts???

Dan

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bkej

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i have an 05 wr450 and the dealer installed a power now valve and also installed an accelerator pump cover (not sure which brand (it is anodized red) along with the rejet. He said that it was supposed to eliminate the bog. Something to do with the way the fuel splashes into that piece?? I'm riding for the first time with the changes today so I will look up the brand on the reciept and let you know how it works.

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Flip01

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I read something on it the other day but can't remember the details. It has something to do with an extra set of holes being mounted higher up in the void in the cover. Or something like that. ?

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Flip01

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quickshot.jpg

Quoted from the Boyesen website:

"Quick Shot Accelerator Pump Cover. Stock accelerator pump covers permit only a 60% - 70% fuel charge in the pump chamber. Turn the throttle and air in the chamber is compressed and fuel is delayed. The result: Hesitation or Bog. The Boyesen QuickShot cover completely fills the pump chamber with fuel, and provides instant fuel delivery, eliminating the hesitation and bog. *Fits all 4-Stroke Keihin FCR carburetors *Instant response to throttle movements *Improved low end performance *Reduced hot engine stalling *No modification required - simple bolt-on"

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Indy_WR450

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Our famous TT member "James Dean" the jetting forum guru recently did a test of the effectiveness of the Boyesen quick shot and said it has no effect other than to simulate a one size smaller leak jet. ? I think it is cheaper to buy the leak jets! ?

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ncmountainman

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i'm still wondering if used in conjunction with the #40 lj that it would'nt totally eliminate bog? JD only tested it with the stock #70 compared to the stock cover w/smaller lj. its getting ordered today i'll let you know in about a week if they work together ?

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SuperRat

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I think I understand how the AP circuit works:

Link screw controls when the pump squirts, the diaphragm controls the amount of fuel pumped (Yamaha sells different diaphragms), and the leak jet controls how much fuel goes through the "bypass" (or how much of the "pumped" fuel actually gets into the engine from the AP). I am not a jetting guy like JD or Indy so take my ideas with a grain of salt. It sounds like the pump cover tries to lessen the amount of air contained with the fuel in the AP, which is a "fix" for a poorly "timed" AP. Setting the timing of the AP is very easy and is explained in your manual. A person really has to know how to adjust the AP because one adjustment affects the other two. Listen to the experts who have spent the time playing with all three.

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Indy_WR450

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Actually, I did disconnect the TPS and found that I lost some low end response.

So I have re-connected the TPS and I am very happy with the way the motor runs.

I experience the same thing. ?

Note: The ACV circuit is really not a problem. It minimizes 4 stroke backfires on decel and its real purpose is to provide a better transition into engine breaking on slick trails! ?

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RADRick

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Our famous TT member "James Dean" the jetting forum guru recently did a test of the effectiveness of the Boyesen quick shot and said it has no effect other than to simulate a one size smaller leak jet. ? I think it is cheaper to buy the leak jets! ?

Not to take anything away from JD, but I believe the Boyesen addresses problems not tested by JD. Significantly, the intial volume and the recharge rate with the Quick Shot cover. I've asked him to respond to this in another thread, but as of yet, he has not. Boyesen is not the kind of company to market smoke-and-mirror fixes.

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tgodwin

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I'm installing the Factory Direct P-38 accelerator cover tonight for the same reason. I believe it is the same setup as the Boyesen. What's the Boyesen cost? The p-38 was a little steep ~$79, but some of the reviews I've read have reseulted in significant decrease in the off-idle bog. It'd be interesting to set them side-by-side and see if there is any differences.

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Seabass

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I'm installing the Factory Direct P-38 accelerator cover tonight for the same reason. I believe it is the same setup as the Boyesen. What's the Boyesen cost? The p-38 was a little steep ~$79, but some of the reviews I've read have reseulted in significant decrease in the off-idle bog. It'd be interesting to set them side-by-side and see if there is any differences.

I just bought one today also, my yamaha dealer guaranteed it would work or he'd refund my money! We'll see ?

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