Ruptured Accelerator Pump

Hey guys,

I've got a 98' YZ400F with a ruptured accelerator pump. Was wondering if anyone has had the same problem and how you fixed it?

Also if anyone has experience on checking valves if you could just give me a few "what to do's" and "what not to do's". I'm preparing for the worst since its so old but who knows.


The accelerator pump is repaired simply by replacing the diaphragm.

Checking the valve clearance is no big deal, but it is bit more complicated if the clearance needs adjustment. The most important thing is getting the timing right and properly torquing the cam caps.

Here's a how to:

...and here's a link to downloadable manuals:

I suggest the 2000 YZ426 manual as the pictures are much clearer and all the specs are the same (except bore size, obviously)

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