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Nubicus
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Recently got a 89 v75 Vulcan and after a lot of cussing and head scratching got it running. Still has a few issues though. One is the petcock is from a four wheeler I think it only has the single fuel outlet and the vacuum line, it runs but it's not right. And there is no air box. Will these issues be a problem? And I'm having a fuel leak on the carbs it seems to be coming from the float body whenever I shut down the bike. And I have to turn off the fuel, also it's backfires and pops a little while idles. Any advice would be appreciated
 

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A few things going on here....

The single petcock should work, but make sure none of the fuel hose is running uphill. Make sure there's no gas inside the vacuum line.

Missing airbox - Does it have filters installed? If so what brand? Knock-off brands can cause problem by blocking ports at the carb throat. K&N and Uni PK92 are the two brands we know will work. Earshaved with pods could make it run lean, which can cause popping. Would need to read the plugs to know where it's at, but first you have to stop the fuel overflow on the carb.

Popping - Along with the above, adjusting the air mixture screws can help. But, has the exhaust been modified? Another source for popping is the "coast enrichers", if stuck closed, will cause popping on decel. Dose of seafoam fixed mine, but you have to fix the other carb issues first.

Fuel overflow - Most likely a stuck float in the carb, but can also be float level adjustment - see repair manual for easy procedure on float level check. Repair manual link is in my signature.

Any open vacuum ports on the carbs, need to be plugged. Open vac ports can cause popping, even loud backfire, like a cannon shot.
 

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Mini thread hijack: I've seen the 'no running uphill' advice come up time and time again, and it just doesn't make sense to me. I'm sure it's become commonplace because it does, in fact, make a difference, but can anyone explain why? Gravity would cause the gas coming out of the petcock to push the gas in the valley over the hump in the line, right?
 

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Mini thread hijack: I've seen the 'no running uphill' advice come up time and time again, and it just doesn't make sense to me. I'm sure it's become commonplace because it does, in fact, make a difference, but can anyone explain why? Gravity would cause the gas coming out of the petcock to push the gas in the valley over the hump in the line, right?
yes it will, to a point. you may have fine flow up to the point in which the fuel level in tank gets close to the highest point of the lines, then it will drop to a trickle, until your finally even with the level of the fuel, at which time flow stops. better off just keeping the flow headed downhill as much as possible

also, many people have put filters on the fuel lines with out trouble, others have had issues. the paper type of filter that is commonly used for this purpose really dont flow too well under gravity feed, and can cause issues.
 

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The fuel flow seems to be a bit on the weak side, even with the hose pointing straight down. The passages in the petcock are fairly small compared to the hoses. Almost everyone that's had trouble with it, ran into fuel flow problems at higher speeds. MTB explained it best, once the fuel level equalizes between the tank and the hose (with the hose looped downward then up), flow pretty much stops.

Just had the same problem with a Polaris that wouldn't start, we cut the loop out of the fuel line and it fired right up. Owner had just done a new carb, fuel line, and a filter, but he had the fuel hose too long. It had been running, then appeared to run out of gas, but wouldn't start after adding gas. (not sure if he filled it completely)
 
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