Quickshot cover vs. BK mod

I know both these mods have probably been covered extensively here at TT but I couldn't find a direct comparison so I'm asking. Maybe they're not even apples for apples so they can't be compared, do they even come close to performing the same task?

I am about to do a little carb maintenance and possibly replace the AP diaphragm in order to cure a stall/bog and thought I might do one of these two mods while I'm at it. I'm a rookie mechanic at best and think the adjusting (not the installing) part of the BK mod might be more than I can handle so therefor the pump cover is definitely more appealing.

they do different things.

bk mod adjust the pump squirt duration.quick shot is basically a bigger pump resevoir.

Which handles a bottom end bog better and why?

bk mod or whatever method of altering the pump squirt.

you need to visually confirm the starting point and length of the pump squirt.

should be about 1 second and start as soon as the slide moves.

not every cabr needs the bk mod.

The 426 was a learning process for Yamaha.

The 98-99 400 is the FCR1 carb, the 00+ is the FCR2 carb. But the 426 00-02 did not get the leak jet in the carb bowl like the 450s and 250fs did. Thus there is not way to tune AP beyond different diaphrams. Thus the BK mod for these bikes was devised.

Now the 250f and 450Fs you just install different sized leak jets (in the bottom of the bowl) to tune the AP - like what the BK mod is trying to do.

But the 426 again was a learning experience. I had one. I ran a JD jet kit with the BK mod and it ran great. no bog. Just had to tune the fuel screw for temp/altitude.

Your other option is to get the 02 AP diagphram and needle and jet the main/pilot from there.

If you want more info on AP and optional sizes, jets etc I can post the link to the Yamaha Technical Seminar info on them.

....link to the Yamaha Technical Seminar info on them.

Please post or IM me the link. Thanks.

AP page 1

AP page 2

AP Page 3

AP page 4

AP page 1

AP page 2

AP Page 3

AP page 4

Thanks.

O.K.....but can they or should they be used together...bk/mod plus boyesen ap cover???!!!

Shure you can use them together, but why? The Quick Shot is for bikes that have too weak of a squirt (I have not met that application yet but maybe a 650 DS bike that primarily is ridden on asphalt?)

The BK mod, leak jets, accelerator pump diaphrams that have a longer stop built into the bottom are all intended to reduce the squirt volume as the street designed Kehein AC pump squirts too long for off road applications.

So doing both is like buying a pair of pants 5 sizes too big and a pair of suspenders, yep you can make them work together.

Shure you can use them together, but why? The Quick Shot is for bikes that have too weak of a squirt (I have not met that application yet but maybe a 650 DS bike that primarily is ridden on asphalt?)

The BK mod, leak jets, accelerator pump diaphrams that have a longer stop built into the bottom are all intended to reduce the squirt volume as the street designed Kehein AC pump squirts too long for off road applications.

So doing both is like buying a pair of pants 5 sizes too big and a pair of suspenders, yep you can make them work together.

So... In street application for a 625 SMC supermoto with a FCR 41 where when you whack the throttle really fast to wide open from a low RPM you get a slight hesitation/stumble or bog for about a half second before it takes off, it would seem the more likely problem has more to do with too WEAK of a squirt and NOT too much squirt volume?

If true, how effective is the Boyesen Quickshot AC pump cover in a street big bore single application? Anybody have experience with this product and how well did it get rid of that stumble?

Sounds like BK mod is more to do with dirt application because tire spins letting engine rev up faster. Is that sort of right?

I don't rightly know if I need bigger pants or just suspenders to hold up current pants.

BTW,

are all of the OEM AC pump covers similar, i.e. offer same benefits?

BTW,

are all of the OEM AC pump covers similar, i.e. offer same benefits?

All of the covers are the same, Kehein makes the pump almost infinatly adjustable. If you want to spend the money for the QS you can do so and adjust the squirt from there, no problem, but you lose and advantage of being able to compare setting with the rest of us as you will pretty much be on your own

While not really wanting to lose the support of the learned and helpful company here, my primary responsibility is to the health of the bike. If the quickshot AP cover has a good track record of reducing/eliminating the annoying stumble, I would, in all fairness to the bike, need to try it. The consequences of it working would mean a lot more riding and not as much time spent here at Jetting.

Has anyone direct experience with the Boyesen QuickShot Keihin FCR Accelerator Pump Cover for such bogging?

If not the quickshot cover, then what could one do as far as the AP diaphram or pump settings?

http://www.boyesen.com/article/articleview/99/1/32

Has anyone direct experience with the Boyesen QuickShot Keihin FCR Accelerator Pump Cover for such bogging?

Replacing the $8 leak jet in your float bowl with a size 1-2 steps smaller will do as much or more than installing the $90 pump cover.

James

Has anyone direct experience with the Boyesen QuickShot Keihin FCR Accelerator Pump Cover for such bogging?

I put the QS apc on my '02 426 (found one for half price at another site) and it made no difference in the bog at the bottom, neither helped nor hurt the situation.

I'm gonna swap it back out and put it in my Husky SM610 to see if it helps a big bore street Kiehin like Hopkins says.?

Replacing the $8 leak jet in your float bowl with a size 1-2 steps smaller will do as much or more than installing the $90 pump cover.

James

What if you have an '02 without a leak jet, can one be installed? And if so is that as good as way to go as the BK mod?

Buy a float bowl with a leak jet installed off JD Jetting.

If a diaphrame is exchanged, does one need to readjust anything due to the shorter rivet ? Like the AP link ?

Does it make sense to try a setup with the diaphrame upside down ? The rivet should be shorter on the other side.

What if you have an '02 without a leak jet, can one be installed? And if so is that as good as way to go as the BK mod?

I think the result of the leak jet and the BK mod is equal. The only down side to the BK is it only works on certain years/models, the FCR1 which Yamaha used in 98-99 it did not work. Your 02 it should work fine, at least on KTM's a change made in 06 eliminted the bass that we drilled for the BK mod.