Accelerator pump

4 replies to this topic
  • hart

Posted February 14, 2002 - 02:41 PM


Alright boys, I know you are just waiting for some schmoe to say something dumb so here you go..

I just got my p-38 and installed it. as I test it with gas in the bowl and move the pump arm up and down(get it "up and down" you can get me here) no gas shoots out the output hole. I notice when I put it all together same deal. What is the one way valve here that sucks gas from the bowl and keeps it from just going back into the bowl?
I know I have a tight fit on the p-38 so I don't think it is sucking air anywhere. Also if I hold the bowl and plug the output hole of the acc pump with my finger when i release the acc pump (making the function of a one way valve) I get gas to shoot out of the output hole.

Go ahead.. let me have it!!

98 wr 400

  • Hick

Posted February 14, 2002 - 03:23 PM


Originally posted by hart:
Go ahead.. let me have it!!

98 wr 400

Trust me, if I knew what you were talking about I would.

Did you put the diaphragm in upside down?

Did you lose the two tiny o-rings that seal both fuel passages (in & out) in the pump?

Did you put the spring back in under the pump diaphragm?

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  • hart

Posted February 14, 2002 - 05:07 PM


in any diaphram pump there has to be a 1 way valve so that the gas doesn't just go back where it came from. That is what is happening here. I have checked all of these things and the spring, diaphram and seals are in the correct place. Does anyone know where the valving action takes place??



  • James_Dean

Posted February 14, 2002 - 05:48 PM


As I recall...
A very tiny check valve (ball and spring) are in the float bowl to prevent fuel from being pushed back into the bowl. Look at the inside bottom of the float bowl for it. It is manufactured into the bowl and is not removeable. Make sure it isn't clogged. Try squirting carb cleaner into it.


  • hart

Posted February 15, 2002 - 05:17 AM


Thanks James! Here is what happened.

I stretched out the diaphram spring (short term fix) and the problem disappeared! I believe that in order to activate the valve you need a sudden "gasp" not a slow one. I think all pressure valves like this need a certain amount of pressure to actuate and I wasn't getting enough pressure (or vacuum depending on what side of the valve you are on)
This mod seems to work well (squirt duration < 1 sec). However if I had it to do over again I would probably do the mod described on TT.. :)


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