Gas Fumes - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 14 (permalink) Old 06-01-2019, 09:21 PM Thread Starter
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Gas Fumes

New to the Vulcan. Lately after a ride I have noticed when I park the bike it smells of raw gas fumes for a while afterwards. I haven’t noticed earlier but now I’m starting to notice it. Is this a common thing or do I have a problem somewhere? I also noticed this one day when the bike was cool but sitting in the hot sun. Is it just pressure in the tank causing the fumes to pass through the vent tube?
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post #2 of 14 (permalink) Old 06-01-2019, 10:09 PM
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I've never noticed on mine, but it's probably masked by my coolant leak. It's probably due to the warmer temperatures, causing the engine to run hotter and heat up the tank.

Check that the hose is connected to the very back of the tank. Normally that runs down to the bottom of the frame (or to a filter in the CA models). If that hose is gone, the fumes are dumped right under the seat.


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post #3 of 14 (permalink) Old 06-01-2019, 10:30 PM
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It could be a lot of things, but most likely either you have a gas leak somewhere, from the petcock to and including the carbs, or it could be from around the filler cap. There is a rubber seal around the cap, and also a rubber grommet toward the back on the cap, near the hinge. Ethanol gas tends to melt rubber seals. If you happen to have a stock bike with the California evap system, there are a ton of places it could be leaking. Best thing to do with those is to completely remove the evap system and vent the tank directly to the atmosphere with a hose that connects to one of the fittings and runs down below the bike.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #4 of 14 (permalink) Old 06-02-2019, 09:43 AM
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Mine does it too, when the gas tank gets hot the pressure rises, the vent system needs a certain pressure to allow fumes to escape so when it does there is a lot of it

Some people have pulled all the guts out of the vent and filled the hole with foam rubber. I have piece of lawn mower air filter sitting ready to do mine as it stinks up the garage when i park

'99 Vulcan "Victoria"
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post #5 of 14 (permalink) Old 06-02-2019, 10:43 AM
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Probably the tank vent, but check the vacuum line on the left carb to make sure it's dry after a run. If it's wet, the petcock needs a new diaphragm.

I haven't noticed any fumes since rebuilding the petcock. However, the bike sits outside until it cools.

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post #6 of 14 (permalink) Old 06-02-2019, 11:15 AM
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Mine has done that for years. Unless I see a puddle, I've come to not even notice the smell. While it doesn't happen every ride, when it does happen its after a ride, or when its been sitting outside in the sun.

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post #7 of 14 (permalink) Old 06-02-2019, 11:42 AM
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If you here a hissing sound from around the gas cap, you have a problem. There should never be more or less than atmospheric pressure inside the tank. The CA evap system is prone to failure, and will allow pressure to build up in the tank. I took my cap apart, took everything out, then put it back together. I did not put anything in it. The tank must be vented somewhere. Remove the seat and see if you have two fittings at the rear of the tank or just one. Either way there should be a hose one it/them. If it has two, then you have the dreaded CA evap system. Get some rubber tubing that will fit the fittings on the tank, if you have two, put hoses on both of them, and run the hoses down through the holes in the frame, and down underneath the tank. Also check that rubber grommet. That is the tank vent. It leads to a passage that exits at the rear of the tank where the hoses go. If it is missing, it would probably leak gas onto the top of the tank when full.

But, I have had several dirt and dual sport bikes that had the vent right in the middle of the gas cap. Again, a vent alone should not cause a gas smell. It sounds more like a leak to me.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #8 of 14 (permalink) Old 06-02-2019, 12:09 PM
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Mine always stunk up the garage after a ride. Sometimes the gas cap would whistle. No leaks and the bike ran fine. I agree if there's no visible fuel leaks or puddles I wouldn't worry about it. I usually turned the fuel tap to OFF when I parked.

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post #9 of 14 (permalink) Old 06-02-2019, 12:17 PM
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Mine has always whistled when parked in the sun, and never a problem, even the new tank with zero miles.

If the petcock diaphragm goes bad, it will leak through the vac hose even when turned to off and not running. The gas will eventually end up in the oil, which makes even more stink.

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Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
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post #10 of 14 (permalink) Old 06-02-2019, 12:24 PM
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The whistling noise is coming from a valve in the gas cap. Take the cap apart and remove the valve, and the whistling will stop. The noise is cause by the valve releasing pressure in the tank. If the tank is properly vented, there should never be any pressure in it. It's part of the emissions control crap. I purged my bike of every tiny little bit of that stuff. My 1997 still has all that crap on it. It is going to be fun removing it. I should box it up and ship it to the EPA.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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