instead of P-38 can you buy the '01 FCR throttle pump?

Is it possible to buy/retrofit the new fcr throttle pump assembly onto the old-style fcr? Get my drift? Why spend $75. on a P-38 when maybe you can upgrade the carb itself for a similar amount of cash? That way you could then do the BK mod, which is superior because its adjustable not fixed.

Anyone looked into it? How much$? Will it work? Bolt on, or no go?

If you do the BK mod, you need not retro fit the accelerator pump. That's the great thing about this mod, you simply adjust the squirt for the best response and you are done. If I had known about this mod, I would not have needed to install the P-38. I will be doing a thorough cleaning of my carb soon and will check the squirt to see if doing the BK mod will add a little more precision to my carb tunability.

Apparently the BK mod can only be done on '01 carbs... not '00 because they are different. Thats what my question is: can the older fcr be updated by buying '01 T-pump parts, so that the BK mod is then possible?

I believe you can do the BK mod on the '00 carb. At least I am planning to. I thought Boit's was an '00 - I don't imagine that particular external body area of the carb would have changed from '00 to '01 - I could be wrong.

Either way - DON'T waste your money on the P38 - it is a gimmick. Yes, I do speak from experience.


Ballistic, to do the mod you must have a 00 or 01 carb. The carb body has a piece molded within the body for the area to be drilled and tapped for the adjustment screw. The 250f carb also has it. Like I said on the "other" forum I will be trying the 250f carb on the "other" 400 soon.

Hey Ballistic,

I have all the models listed on my site that will work CLICK HERE for the BK carb mod page! I was looking at my friends YZ400 carb and you could do the mod to the accel pump, but it wouldn't be in the form of a screw/spring combo. This is because their is not a tab extruding off the side of the body of the carb. Since there there is no place to drill and tap a screw...someone would have to get real creative. Hope this helps,


This Modification is only for the 00'-02' YZ426, 01'-02' YZ/WR250F and 01'-02' WR426...this modification WILL NOT work on 98-99 YZ400's and 99-00 WR400's


I get my kicks on a 426!

Motoman393's MX Site

[This message has been edited by motoman393 (edited September 02, 2001).]

"This Modification is only for the 00'-02' YZ426, 01'-02' YZ/WR250F and 01'-02' WR426...this modification WILL NOT work on 98-99 YZ400's and 99-00 WR400's"...

Thanks Motoman... thats what I was trying to say. Let me restate my question, because I think some are misunderstanding:

According to Motoman, and other posts I've read, the BK mod will NOT work on YZ400 or WR400 carbs, because the carb is different in some ways. THEREFORE... is it possible to purchase from Sudco the new-style (e.g.YZ426) throttle pump assembly, and retrofit it onto WR400 carb. Why? Because then the WR400 carb could then get the BK mod.

Is it possible? And if so, would it be reasonably easy to do? Because if the answers are YES and YES, this would be superior to buying the P-38 thing.

The YZ/WR 400's carb is a completely different body than the YZ/WR426's! You can replace the body but that is expensive and is like putting a whole new carb on your bike, so it would be a waste of money! I have a friend who rides a 01' KTM520SX and they have the same carb as the YZ400 does, and he somehow put an adjustable screw on his. Whenever we ride next I will ask him to show me how he did it...and maybe you guys with YZ/WR 400's might be able to do the BK mod!



I get my kicks on a 426!

Motoman393's MX Site

thanks moto.

I looked at your pictures, I see its alot different. But I see on my carb that I could rig a bracket to hold an adjustment screw.

BTW, my bike strangely enough is a DRZ400, which has the same FCR as the WR/YZ400. No one on the DRZ chat room is doing much in the way of carb tuning... so I mosied over here because obviously you guys talk ALOT about carbs.

LOL let us know if you get it to work on your carb! And if you do "shed some light" over at the DRZ forum! Im sure the BK mod would be a very popular mod for the DRZ as well! If you get some pics I will put them on my site of the DRZ BK mod! Later,



I get my kicks on a 426!

Motoman393's MX Site

Oops. I didn't realize that you meant a pre '00 FCR carb. Yes, mine is a '00.

Before anybody discovered how Tim Ferry’s mechanic had managed to shorten the accelerator pump (he posted about it then left us to figure it out, not to toot my horn but I did :) ), James Dean on the WR side just drilled and tapped a hole in the bottom of his pump cover, dead center. This method will work on any FCR.

The center portion of the pump diaphragm then bottoms on the screw and not the cover, turn the screw in and the pump stroke is shortened. The obvious drawback is you are drilling a hole into a part that holds fuel :D

I’m sure some type of sealant would take care of that, maybe a post on the WR side would scare up JD (or a search may uncover his original post) plus replacing the pump cover isn’t a huge deal (I think they are like twenty five bucks?).

Finally, a few of us (James, myself, maybe somebody else) tried a few different times to order the optional pump diaphragms that appear on the ’99 and ’00 fiche, suspecting that they had longer and shorter center portions to alter the pump stroke.

Nobody was ever able to get these parts, but it has been a while since we tried. I did note that the metal insert on my ’01 (standard or stock) diaphragm was actually shorter than my ’00, so don’t go that route, this also makes me wonder how well the Fact. R&D cover would work, if at all, on an ’01.


[This message has been edited by Hick (edited September 03, 2001).]


I have not yet taken my carb apart, but have seen the bottom of the pump. (not the inside) Could the pump stroke be adjusted by using shims under the diaphragm?


Rick Fuller

'01 yz426

'00 yz426 destroyed by fire in desert race 4/22/01

'81 490 Maico

Yes, I think that would work. I'm not sure it has been tried, but I don't see why it wouldn't work.

You would just need to make sure the shims are small enough to not interfere with the in/out fuel passages integral to the cover while still being large enough to remain between the center portion of the diaphragm and the cover.

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