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Carbs and Fuel System
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post #1 of 13 (permalink) Old 05-01-2007, 10:42 PM Thread Starter
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What I've learned.

Hi everyone,
I am new to these forums. I just bought a '92 VN750, and am having a problem with fuel flowing out of the carb vent hose behind the right air filter assembly. I have read through almost all of the threads which look to address similar problems, and between what I've read and what I figure the problem to be, I think I have found the problem and solution.
Sounds to me that there is a stuck float or float valve. I have put several ounces of SeaFoam in a fresh tank, and run it through, let it sit a day, and noticed the motor starts better, but the fuel still flows out of the vent, maybe even more now. I noticed that the bike runs really well when I turn the petcock to OFF, that is, until it runs until it conks out from running out of fuel. Also, no fuel comes out of the vent hose with it on OFF. When I turn it back to ON, the bike sputters, runs rougher, and the fuel comes out of the vent hose.
A little history on the bike. One owner, meticulously serviced. Was put away 2 years ago and not ridden or even started due to an injury. Previous owner says she put Sta-Bil in when she stored it, and prior to that it always started easily and ran like a top. (This is a good friend, and I have seen the bike when it was running, so I know this to be true.)
So, I am planning to try again tomorrow, after the SeaFoam has sat another night, and if it's not better, I will drain the tank, and run straight SeaFoam through the carbs, let that sit for another day or so, and try again. I would rather not pull the carbs unless absolutely necessary, as, like I said, I can get the bike to run really well with the petcock OFF. I pulled the petcock, and cleaned it, and it works properly. I also removed the gas cap, cleaned the vents on that, and made sure the vent line for the tank was clear as well. Does anyone have any other suggestions for me?

Here's a little history on my bikes. I also have owned an '86 VN750, so I am fairly familiar with the workings of these bikes, as I had a chore keeping that one running well. During my searches on these forums, I've noticed several people mentioning the fuel petcocks, and there seemed to be some confusion. The '86 had a PRI-ON-RES, while the '92 has OFF-ON-RES. They switched to that one starting with the '90 models, I believe. The PRI setting does stand for PRIME, and allows the fuel to flow without a vacuum, without the motor turning over. I am intimately familiar with this because I also own a Yamaha Virago which also has PRI, and I left it sitting for the winter on PRI once. When I tried to start it in the spring, the starter would not turn the motor, as if it was seized. The cylinders had filled with fuel, I simply had to pull the plugs and crank it a few times to clear them, but that was 700 cc's of gas wasted, heh.

Well, if anyone has any other ideas for me before I decide to pull the carbs, I would appreciate it. Thanks.

Last edited by medic274; 05-01-2007 at 10:45 PM.
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post #2 of 13 (permalink) Old 05-01-2007, 10:49 PM
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I agree with you , sounds like the floats are stuck. Sometimes tapping on the carbs will help free them up.
You can drain the carbs and put straight Sea foam through the drain tube.
It should be a allen screw to drain the carbs, it will come out of a nipple on the bottom of the carb.
YOu can put on a small hose and fill the float with sea foam from there.

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post #3 of 13 (permalink) Old 05-01-2007, 10:55 PM
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I'm just guessing here, but it sounds almost like a float problem as you have said. If the float is puncured it will fill with fuel and never float. The valve will remain open and thus you end up with a flooding issue. Maybe someone else here has run into the same situation as you and will chime in. Good luck regaurdless.

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post #4 of 13 (permalink) Old 05-02-2007, 12:44 AM Thread Starter
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CCSpinner, thanks for that, I may try pushing the SeaFoam up the drain hole. My drain screws are philips head, though, so no problem with stripping them. They turned freely enough when I checked the levels, which, by the way were within limits, or maybe even a little low on the rear carb.

Foxhound, I hadn't thought of that. The only carbs I've had apart are the ones on my Virago, and the floats were foam. I never considered that the Vulcan's might be hollow. Can anyone confirm if they are?
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post #5 of 13 (permalink) Old 05-02-2007, 09:08 PM Thread Starter
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OK, today I drained the carbs and sprayed Gumout up the drain holes until it came out the vent hose. I added more SeaFoam and ran that through a bit. Still had the same problem, would run fine with petcock on OFF, but when I turn it to ON, the engine runs rough and sputters, and fuel comes out of vent hose. I even put a clear hose intot he vent hose and taped it to the handlebar, so the open end was above the tank. Fuel would run only as high as the level in the tank. (actually made a neat fuel level gauge) So, I decided to bite the bullet and pull the carbs. Opened them up and, sure enough, the front carb float valve was all gunked up. The rear carb float valve looked OK. Both lower bowls had a coating of varnish on them. Gave each a good cleaning, so they should be as good as new now. I hope that does the job. I will be putting them, back in on Friday, and will let you know if that works.
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post #6 of 13 (permalink) Old 05-02-2007, 09:12 PM
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That sounds promising. Good find. Nothing beats taking the carbs apart and cleaning them.

Let us know you good results Friday.

Jon

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post #7 of 13 (permalink) Old 05-02-2007, 10:11 PM
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I haven't been in my carbs yet. Are the floats solid or hollow? I know the tecumsa carb on my mower uses a hollow metal float.

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post #8 of 13 (permalink) Old 05-02-2007, 10:21 PM
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Quote:
Originally Posted by Foxhound View Post
I haven't been in my carbs yet. Are the floats solid or hollow? I know the tecumsa carb on my mower uses a hollow metal float.
I didn't poke at mine to find out for certain, but they look and feel like hollow plastic.

C
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post #9 of 13 (permalink) Old 05-02-2007, 10:35 PM
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Haven't been in the carbs yet either, but every carb I've seen has a hollow float - thus the floating part <g>


One of these days I have a feeling I'd do well to pull the carbs and give em a good cleaning - seafoam is great but nothing beats actual manual cleaning of the working bits...

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post #10 of 13 (permalink) Old 05-04-2007, 12:10 AM Thread Starter
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I can confirm that the floats are hollow plastic.
I know that the floats in my '85 Yamaha Virago 700 were a solid, plasticky foam.

One thing that I did do before I closed up each float chamber was blow gently into the fuel hose while lifting and lowering the float, and making sure it would seal and that it opened when the float's centerline was between the two marker tabs. I don't want to have to pull those carbs again just to adjust the float levels.
Once I cleaned the coating of varnish off the parts, everything looked like new, so I didn't feel that a rebuild would be necessary. I can't imagine this NOT doing the trick, but will find out tomorrow. Wish me luck
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