YZ426F Accelerator Pump Problem

3 replies to this topic
  • mark794

Posted March 29, 2005 - 10:40 AM


I've got a 2002 YZ426F with a Keihin 5JG6 500 Carb on it, that has a flat spot on low RPM acceleration. It started on my last ride. I ordered a Factory R&D P-38 for it figuring it would cure what was happening. When I pulled the Carb it appeared that the Pump wasnt working at all.
Yes, the bowl was full and all the passagways were clear EXCEPT when I tried to Push some B-12 chemtool through the port in the body to the spraybar it appears clogged. My question is... Does there need to be venturi/manifold vaccum in order for this to work? I was under the impression the the pump was like an automotive type the will squirt as long as the bowls are full but i'm not sure about this one. Is there some type of valving in the lower part of the main body that doesnt show up on the factory exploded view of the carb? I noticed that the Lower part of the main body is removable (4 screws) between the float bowl and main body that has factory
sealed screws and dont want to split if if I dont need to. On an added note is B-12 chemtool too hardcore to use on this type of carb?
Thanks in advance to any replies/info anyone has.

  • Fastest1

Posted March 29, 2005 - 03:41 PM


DO NOT FOR ANY REASON UNDO THE SCREWS THAT ARE SEALED! THAT GASKET IS NOT AVAILABLE. The Chem tool should be fine. How does the diaphragm look? It should spray a fine stream (very small) while holding the entire carb in your hand (watch the eyes)

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  • mark794

Posted March 29, 2005 - 03:59 PM


I was afraid of that, which is why i didnt break it down that far. Everything is in good shape except the plugged section of the body. I was more worried about the chemtool affecting the TPS if it was to make contact. I read an earlier post that leads me to believe i should be able to unplug it. Thanks for the Input.....

  • Fastest1

Posted March 29, 2005 - 11:07 PM


The TPS is not mandatory for operation. Tim Ferry's bike never ran one when he was riding the 426!

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