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I am having trouble with the vacuum petcocks


MasonHart
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I do not think there is any vacuum being created on the left side because with all the lines hooked up and with the bike running fuel will not flow on the left side. I can see both side because there is a clear filter on each side.

If i take the line off on the petcock side of the filter fuel will run out of the tank no problem. But when the bike is on and running with everything hooked up there is no fuel flowing on that side. The other side is perfect.

Is this an issue with the carb not producing vacuum? Or something weird with the petcock? Or possibly a problem with another part?

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The carb doesn't produce vacuum. The cylinder does, so yes, the petcock probably needs to be rebuilt. Or better yet, replace it with an on/off/reserve (non vacuum) petcock. These vacuum petcocks are notorious for failing...mine did.

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you can test the petcock sometimes just by sucking on the vac line that goes to the manifold and watching for fuel flow

yea, give it a blow job B)

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Could it be a problem with another part of the bike? Because when i connect the line that comes off the petcock gas will pour out just fine but it doesn't ever make it to the carb. It wont even fill up the inline filter.

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My question would whether it runs well. On my bike, at times the fuel filter will get low when I am riding, but there is always gas flowing through it. I say if it runs fine, don't worry about it.

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It isn't starting now that i found this problem. I can hit the start button and it starts cranking but it wont start. Yesterday it was starting only if i hit the start button and held the throttle open some. Then it would run but not great. Only on the left cylinder i am sure. And it wouldn't idle all the time, if i let go of the throttle it would slowly decrease in rpm's then die. If it did idle it was vibrated a lot and if i hit the throttle it would very slowly decrease in rpm's back down to idle.

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It isn't starting now that i found this problem. I can hit the start button and it starts cranking but it wont start. Yesterday it was starting only if i hit the start button and held the throttle open some. Then it would run but not great. Only on the left cylinder i am sure. And it wouldn't idle all the time, if i let go of the throttle it would slowly decrease in rpm's then die. If it did idle it was vibrated a lot and if i hit the throttle it would very slowly decrease in rpm's back down to idle.

sounds like its 'running on one', to find out which side is easy, the exhaust is hot on just one side ;)

DONT BURN YOURSELF CHECKING !

;)

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Well i would test that BUT, it wont start no. I think it is flooding because the PO did something with the petcocks and just told me to keep it on prime all the time. But when i was emptying the tank i was getting flow in all positions. But then it would just be acting as a manual petcock. So it should should still give gas to the carb, right? One would think so., But it doesnt have enough force to get it to the carb. The gas stops flowing before the carb.

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If you're getting flow but it's not getting to the carb, it must be your filter. Pull it out and see if it will fill the carb. If it doesn't, put it on prime and see if it is vacuum causing the problem.

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Well its not the filter because i took it out and cleaned it and the problem is still there. The other side is fine with the same exact filter in the same place, except that line is direct to the carb, on the right side it has to go uphill to get to the carb. And the PO said that he did something to the petcocks so i should leave them on prime all the time. So it is acting as a manual petcock now correct? Since prime just lets fuel flow without vacuum. I am guessing that it needs that vacuum to get pushed uphill right?

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