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Old 10-26-2011, 03:42 AM
klx650sm2002's Avatar
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Accelerator pump question

Hey guys
I have a pumper carb on my 650 4 valve single, the pump volume is 3.5cc (which is about a 3.5 second squirt) which I think is a lot. The only adjustability is, the linkage which strengthens or weakens the initial part of the squirt, the accelerator pump stop screw which can reduce the squirt to nothing, and it is possible to put an O ring on the linkage to suppliment the spring.
At the mo I'm on the stronger linkage setting no O ring and about a 1sec/1cc squirt.
What do you guys think ? should I go lower ? I'm in the process of fitting a logging wide band lambda sensor Which might answer my question!
Thanks in advance
Clive W

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Old 10-26-2011, 06:23 AM
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What function does the spring have- is it an 'override' spring to allow full throttle w/o jamming the pump and/or linkage? Because if it is, it could be shimmed some, but going too far will cause problems because fuel is non compressible, if you try to compress it, something will give.

If it's a pump return spring, just be sure it's not going to over power the override spring, or you won't get the full pump shot.

In any event, an O-ring is rubber and would not wear well at all in any sort of application where it was subject to friction/wear. A possibly better solution would be to use a more wear resistant shim material.
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Old 10-27-2011, 08:03 AM
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Hi Cobalt
Yes it is an "override" spring and yes there is a pump return spring but it's much weaker and not a problem. The "o-ring mod" is quite common but yes it does need replacing often, bike goes better without it. Will try to post a pic. Screw and lock nut is right at bottom of carb.
Clive W
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