01 YZ426- Accelerator pump Question


Big CR man

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May 17, 2001
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I was Reading my new MXA magazine and they had a write-up on Tim Ferrys YZ426 . They said his bike starts on the first kick every time . He runs a production carb without an accelerator pump on it . If this is true than why even bother with the BK Mod . Cant a guy just remove the accelerator pump or unhook it altogether. ???? I'm no genious when it comes to carbs, so please don't think I'm foolish . Just trying to learn . Thanks in advance for any input I recieve.
 

Boozer

Member
Oct 5, 2001
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if you remove the acc. pump on your Flat CR carb, the bike will die when the throttle is cracked from low engine speeds. since the slide is directly affected by throttle position, the motor will ingest a sudden and large amount of air during quick throttle openings. this causes a lean mixture and the engine will die. i know this because my bike had an unreliable and short pump squirt from the factory. i now have it shooting for about 0.5 seconds and it runs fantastic. the throttle can be hit from idle, and the engine will not bog or hesitate.
if Ferry runs a carb without a acc. pump, then im guessing it's some kind of CV carb. the slide position in a CV carb is controlled by engine vacume instead of throttle position, so it is possible. not sure why they changed the standard Kehin. oh, and it is easy to disconnect your acc. pump to see for yourself. probaly the easiest way is to remove the diaphram pushrod. access can be made via the diaphram assembly.
 

VintageDirt

Baked Spud
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Jan 1, 2001
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I believe MXA said Ferry runs it without the throttle position sensor.:)
 

Big CR man

Member
May 17, 2001
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Ferrys mechanic

I think your right. I'm not sure why he came up with the BK Mod . I understand that he came up with this Idea , but why now are they running without an accelerator pump altogetherSee page 42 on April 2002 of motorcross action magazine in the upper left picture it reads : One Kick: Ferry runs a heavily modified production carburator. most notibly, it is missing the Throttle Position Sensor.We could start Ferrys bike without the Hot Start button on the first kick EVERYTIME. Please Someone tell me what is up . Can a guy just remove the throttle position sensor instead of the BK Mod . I know there are many Experts in this field . Please Let me Know , This is driving me crazy . Im fouling plugs all the time . I traded My CR Two Stroke in on a brand new bike that I cant start unless I install a new plug first . I'm starting to miss how easy and reliable of a starter my CR was .My appologies to BOOZER I wrote this post before I saw your Explanation on this matter. It still looks like his carb is the same as mine . other than the TPS is missing off the side .And also thanks to Vintage Dirt for clearing up what I said. I meant to say TPS but I wrote accelerator pump .
 
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Big CR man

Member
May 17, 2001
35
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Gosh I feel stupid

What i wrote earlier is that Ferry runs without an accelerator pump . What I meant to say was Throttle position senser. can a guy run without this or should he just do the BK Mod.??? once again please forgive my Ignorance .
 

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