Kawasaki VN750 Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
53 Posts
Discussion Starter #1
Today riding to work i heard what sounded like a backfire then i had little throttle response. I was hearing popping sounds then but could keep up speed with full throttle. Then i started losing speed with no way to stop it. I pulled off at the next exit to see what cylinder was gone and when i did both cylinders were firing fine and i had full power. now it sounds like i have extra air coming out the exhausts. Also when i give it some gas at idle, when it revs back down it sounds like something is winding down after the engine has already revved down. Any thoughts or info would be helpful. It is an 85 so i know it is an old bike, but it only has 17000 miles on it. Thanks Mick.
 

·
1986 VN750
Joined
·
3,255 Posts

·
Registered
Joined
·
53 Posts
Discussion Starter #3
I thought that maybe too, but by the time i had come to a stop i had full throttle response. from the stickyon that it doesnt sound like that to me maybe the more knowledgeable can give a yes or no
 

·
1986 VN750
Joined
·
3,255 Posts
I thought that maybe too, but by the time i had come to a stop i had full throttle response. from the stickyon that it doesnt sound like that to me maybe the more knowledgeable can give a yes or no
I have never experienced it personally so I can't be of any more help. I am sure somebody here has seen and tackled this one before.
 

·
Registered
Joined
·
3,353 Posts
I did experience POOGS, and it sounds a lot like what you described. If you hear hissing from the gas cap, then you may have POOGS.

You may not have a totally clogged vent so at idle it may seem to run right, but at highway speeds, the flow of fuel can be restricted by the vaccum created in the tank, thus starving the engine of fuel.

One way to test it is keep a spare key in the gas cap and flip it open if it happens again. if opening the cap returns the engine to proper running condition at speeds, then it most likely is POOGS.

Backfire comes from running too lean, and starving the engine of fuel is definitely a lean condition.

In my case, the vent tube hanging out the bottom of the bike had what I can only describe as a "tar ball" on the end of the hose which was partially clogging the vent hose.
 

·
Premium Member
Joined
·
3,026 Posts
If you hear a "hissing" sound coming from the gas cap, you definitely have a venting problem. There should never be any pressure or vacuum in a fuel tank. If it is a CA model you have a nice option for fixing venting problems, if it isn't, try removing the valve from inside the gas cap, and the rubber grommet at the back of the fuel filler.

The Vulcan is prone to starting up and running on one cylinder for over 30 seconds after sitting for a few days, I think it is a fuel supply problem caused by the vacuum petcock. Both my Vulcan 750s have done it. But not while running out on the road. I did have a problem once where the rear float was rubbing against the float bowl, and would stick, sometimes in the up position, sometimes in the down position, resulting in both flooding and fuel starvation at the rear cylinder.
 

·
Registered
Joined
·
53 Posts
Discussion Starter #7
Well no problems since the initial one. I am not hearing any hiss from the gas tank. the air noise i was talking about is coming from the exhaust. it just sounds like i short breath of air out the back. I have the air mix screws out at about 2 3/4 due to the p/o putting straight pipes with screaming eagle pipes on them. im not sure if thats a normal sound with that setup. Another thing is i just refueled and i got 38 mpg for the tankfull. thats pretty low considering i normally get high 40s.Thanks Mick
 

·
Registered
Joined
·
77 Posts
I was on my way home last night and the same thing happened to me. It seemed like it was running on one cylinder, I gave it more gas and it had no power what so ever, so I looked down at my petcock and it had been turned straight down, which I presume is off on my bike, as I turn the tab back towards the rear fender to turn the fuel on on mine and tab forward facing the front fender if I need to go to reserve. With all that said I turned the petcock back on and it went right back to normal. Some punk at work must have felt frisky with my ride. Just Something that happened to me that is awful similar to your situation.
 

·
Registered
Joined
·
619 Posts
I was on my way home last night and the same thing happened to me. It seemed like it was running on one cylinder, I gave it more gas and it had no power what so ever, so I looked down at my petcock and it had been turned straight down, which I presume is off on my bike, as I turn the tab back towards the rear fender to turn the fuel on on mine and tab forward facing the front fender if I need to go to reserve. With all that said I turned the petcock back on and it went right back to normal. Some punk at work must have felt frisky with my ride. Just Something that happened to me that is awful similar to your situation.
Back to the rear fender is usually off prime on my 86 model straight down is on and forward reserve
 

·
Registered
Joined
·
77 Posts
And that is how mine is labelled, but that is not the way it runs. I found this out on my very first ride driving it home from buying it. It started to spit like it was out of gas, I reached down and turned the petcock forward to the reserve tank and it caught back up, so I reached down and flipped it back straight down and in just a few minutes it was spitting again, so I flipped it back forward to the reserve tank. It caught back up and at that point I flipped it all the way back and has been running great ever since, until somebody flipped it down at work and on the way home it ran like it had lost a cylinder, I looked down and the petcock was facing straight down. I flipped it back towards the rear again and it caught right on back up. Maybe the hoses are hooked up backwards or something. I don't know.
 
1 - 10 of 10 Posts
Top