JD, some hep on the varying diaphragms for the accel pump.

JD and everybody else,

Do you know how the yamaha part numbers for the AP diaphragms coincide with the stroke travel of the accelerator pumps?

I see the following diaphragm part #'s:

5BE-14940-15-00 (YZ ONLY)

17 (standard on the 99 WR)



There is no standard listed for the 99 YZ...

Do you know which one has the most limiting AP stroke?


'99 WZ with all YZ mods, FMF PowerBomb header, Stroker SX-1 silencer, SS front brake line, forked over by Pro-Action, OEM YZ tank and IMS seat.

Last summer the local bike shop tried to get all of the optional pump diaphrams for my '00 WR and they were not available from Yamaha. It is still a mystery what the differences are.

The stock diaphram height, 8.1mm, does not limit the stroke, the cam profile does not stroke that far. At a height of ABOUT 8.5mm it would start to reduce the 3mm of stroke.

Anyone else?


JD: When I first read your response about the "Cam" profile.....at first I thought you meant the camshaft. Well, obviously you meant the little plastic cam on the carb slide shaft that operates the accelerator pump plunger rod, right? I had a brain burp.... :)

Yes, that was the plastic cam on the carb linkage. :)

Does anyone know if the 2001 models use a different plastic cam to alter the pump stroke or timing?

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