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Ok everyone,

I have a cross state motorcycle ride to Northern MN tomorrow and I'm very excited for that. But I've run into an issue. After putting in new spark plugs and reinstalling the tank, I filled up the tank. While I was at it I topped of the oil and tried to start the bike. But it wouldn't start. It would if I ran with it and popped the clutch.

Oddly enough it will start and run fine on "Res" setting from the petcock but not "On". It's not a vacuum issue is it? I figured not since I thought both "Res" and "On" would require the same vacuum pressure to operate. Wouldn't it make more sense for the lower "Res" straw from the tank to be clogged? I cant think of why the "On" setting won't work.

What should I check?
 

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start by removing the petcock, see if the little filter is not dirty, and if its clean open the petcock, because the ON passage may be, clean it and install it back, see if that solve your issue.
 

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Remove tank and set it on bench and support it well
Take the vacuum hose and put it back on the petcock--suck gently on the vacuum hose and gas should flow in both RES and ON positions--they should not leak any when not under a vacuum! It doesn't take much vacuum for the gas to flow (NOTE: prime position will flow freely without any vacuum)
If gas does not flow in either position; do as doitmanny suggests--check the screen; if screen ok then disassemble petcock--it's plugged so clean it
Hopefully you will not need a new petcock--but I've replaced a many of them!

Or go on hour ride in the RES position and just fill up a little more often--no biggie--deal with it when you get back

Let us know what you find so others can learn
 

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Remove tank and set it on bench and support it well
Take the vacuum hose and put it back on the petcock--suck gently on the vacuum hose and gas should flow in both RES and ON positions--they should not leak any when not under a vacuum! It doesn't take much vacuum for the gas to flow (NOTE: prime position will flow freely without any vacuum)
If gas does not flow in either position; do as doitmanny suggests--check the screen; if screen ok then disassemble petcock--it's plugged so clean it
Hopefully you will not need a new petcock--but I've replaced a many of them!

Or go on hour ride in the RES position and just fill up a little more often--no biggie--deal with it when you get back

Let us know what you find so others can learn
correct here, check it first, make sure you vacuum line its connected where it needs to be in the carb, and that its not broken.
hope you dont have to replace the petcock - i have replace then like 4 times on 4 different bike as well. in other case you can get a rebuild kit if is not plugged and rubbers are damage. this will save you a bit of cash
 

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if you end up needing a new petcock, i found an OEM replacement for a reasonable price when i went to replace my leaking one at niche cycle part number 51023-1260
if you don't want to fork out that sort of money and are up for putting new seals in, i can send you my old one.
 

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So what you're saying is that if the gas line hose is disconnected and the petcock is in the run position there should be NO leakage of gas. Gas will only flow if the smaller hose is creating vacuum. My petcock is dripping and causing the gas to flow down and appears to going into the crank case. If I pinch off the flow hose below the Petcock all seem to be good. Bad Petcock/dirt in the petcock ??
 

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inside the gas tank there is a tube connected to the petcock, the tube is divided to allow fuel for ON dial position and RES dial position, the RES position also feeds the PRI dial on the petcock, maybe the section on the tube feeding the ON dial position is plugged
 

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inside the gas tank there is a tube connected to the petcock, the tube is divided to allow fuel for ON dial position and RES dial position, the RES position also feeds the PRI dial on the petcock, maybe the section on the tube feeding the ON dial position is plugged
cant see any tube inside the tank connected to the petcock. We're talking about a 96 VN800B the only tubes connected to the petcock are outside the tank Vacuum from Carb and fuel line to carb.....I have a vacuum feed petcock that the bike must be running creating a vacuum to open the diaphragm to allow gas to flow. I believe the Diaphragm is either torn or just worn out
 

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not outside the tank but inside it, is there not a solid tube connected on top of the petcock and is inside the gas tank?
 

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yes there is a solid tube but that zilch to do with the actual feeding of gas . I am talking about the petcock itself and the diaphragm that opens and closes the fuel flow. After 20 years I believe this is going to be the main culprit so it's either rebuild the vacuum or go to a std 3 position petcock like on the newer Vulcans
 

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took the petcock apart and rebuilt the entire thing. Now there is NO flow when in the RUN position except when the engine is running thus opening the diaphragm.
 
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