Author Topic: Walbro HD 34A accelerator pump  (Read 59 times)

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Offline kr5258

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Walbro HD 34A accelerator pump
« on: January 11, 2016, 08:47:02 pm »
Having a tuning problem with a MS361. Carb tunes normally on the low side but I can't get enough fuel into it on the high side. The saw runs up close to 15k no matter how many turns out on the H screw. Carb swapped from another MS361 and saw tunes normally.
The problem carb has been kitted and thoroughly gone thru. I suspect the accelerator pump circuit is pulling air in past the pump piston. Pump piston shows scoring just as I have seen on the problematic MS200t ZAMA C1Q-S126 accelerator pump.
Can anyone verify this theory before I plug the pump bore to test (and give myself another project trying to get the plug out)?

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Offline jmester

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Re: Walbro HD 34A accelerator pump
« Reply #1 on: January 11, 2016, 10:17:47 pm »
From what I understand if the pump piston is scored it will not hold a vacuum behind the pump piston to draw fuel from the metering side of the carb. I am not sure if it feeds fuel the hole time the throttle is open or just when you first depress the throttle.
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