Faulty petcock? By worzx (Read 383 times)

[worzx]

Hello all,

I have a Longjia LJ50QT-3M chinese scooter with a 4-stroke 139qmb engine. I am experiencing an issue where after few minutes of driving, the throttle falls back to idle and bogs down after I stop. I have to wait a few minutes then I can go forever. This happens randomly.
I had a tip that it might be an issue in the fuel system (petcock and fuel filter). Today I checked them. As far as I'm concerned, a vacuum petcock should only allow fuel flow when the engine is running and the vacuum in the carb sucks through the vacuum hose which connects to the petcock. However, I pulled down the fuel hose from the fuel filter and definitely got more fuel than what could be in the filter and the hose.

Is this normal?

Also, do you have any ideas about the issue?

[trashtruck12172]

could be a bad diaphragm in the petcock. you could gravity feed the fuel with an inline fuel shutoff, remove the petcock and block the vacuum source at the manifold.

[worzx]

Jun 29, 2016 17:12:31 GMT -6 trashtruck12172 said:

could be a bad diaphragm in the petcock. you could gravity feed the fuel with an inline fuel shutoff, remove the petcock and block the vacuum source at the manifold.

Thanks for confirming. I thought about just getting a manual petcock and just putting it somewhere, maybe above the filter and finding a right place for it. Do you think that is the source of the problem I mentioned?

[trashtruck12172]

bypass the petcock with an external fuel source, (gas can)and gravity feed it with a hose to the top of the fuel filter or directly to the carb. this should let you know if the petcock is bad or not. remember to block the vacuum source.