Question about accelerator pump timing screw...

5 replies to this topic
  • Pooley

Posted July 22, 2002 - 05:35 PM


I have not done the BK mod but have been reading that the timing on the acclerator pump is correct when the stream of gas just misses the slide. Is this information correct?

I was playing with the timing screw when I had the carb off today and noticed that the squirt does not come anywhere near the slide even when the timing screw is all the way in or out, (and yes there was gas in the carb). The squirt would start at approximately 1/2 throttle with factory settings and all the way out. Squirt started barely at full throttle with it all the way in.

Is this abnormal since it never even comes close to the slide, or just be happy and leave it alone?

Thanks for the help.

  • MN_Kevin

Posted July 22, 2002 - 11:08 PM


your timing is indeed correct, however be sure and check the squirt duration. Concesus and BK recommends < 0.5 seconds.

  • michaeltrundle

Posted July 23, 2002 - 02:03 AM


Half throttle is way too late!
Please someone, correct me if I'm wrong but-
Your squirt should start as soon as you crack the throttle open, not at half throttle or later. There is no point having a spit of fuel after half throttle at all.
The AP is there to give you crisp throttle response by spitting in a dash of fuel when you first crack open the throttle.
At low rpm there isn,t a continuous or strong enough stream of vacuum pulses being created by the engine to accurately suck the required amount of fuel out of the pilot jet when you crack it wide open. All you get is a lean "bog" as the engine sucks too much air and not enough fuel.
This is when you want the AP to spit a dash of fuel in and then stop, once she starts to boogey.
By the time you get to half throttle the engine should be wound up and sucking harder and more cosistently. The required amount of fuel is pulled out of your jets more accurately at higher rpm due to the stronger and more frequent vacuum pulses created by the engine. Therefore not requireing an unmeasured amount of fuel coming out of the AP nozzle confusing your upper midrange jetting.

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  • skthom2320

Posted July 23, 2002 - 07:37 AM


I agree. If the AP squirt starts so late (1/2 throttle), then something may be wrong.

However, did you have an off-idle bog? If not, put the AP pump screw back to where it was and go on!

If you have an off-idle bog, then we will have to readdress the issue...

  • rob1980

Posted July 24, 2002 - 01:57 AM


My AP squirt on my 250 was just hitting the slide, so I adjusted it so it just misses the slide when you give it a good twist.
Definately doesn't start at half throttle.

  • Pooley

Posted July 24, 2002 - 04:09 PM


Thanks for the responses, but what should I do about it not being correct. Call me anal retentive but eventhough the bike does not seem to have any real problems I think it should be corrected.

I have found that when wheelieing at low speeds to loft the wheel over logs and debris that its very difficult to predict when and how hard the wheel will come up, and when it does it is in no way controlled. I suspect it is due to a big burst of fuel and not my technique. I am not a racer or real aggressive (yet) :D and ride trails and woods. The last thing I want is to get a burst of fuel at 1/2 throttle in 36" wide trails!

Does the BK mod and the limiting of the acc pump also affect when the squirt starts? Something inside the carb may be plugged, bound or otherwise not functioning?

Like I said earlier, even if it causes no major problems I will know its not correct and it will drive me crazy...And no one needs an obsessive, sleep deprived rider anywhere near them. :)



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