I have a 98 vn750 that has about 45k on it. here is what it is doing. If new plugs are in it and everything had been drained from the carb I can get about 100 or so miles before the carb starts dumping too much fuel into the front cylinder. I thin this because the plugs are fouled with extra gas residue (thick fluffy looking black stuff) Once the plugs are fouled the front cylinder goes out completely. I have taken the carbs out and cleaned them multiple times, adjusted fuel air on them, checked the jets, float Ext. I still con not seem to find the problem. At one pint I thought perhaps I had a coul doing out so I switched the rear coil and the front to see what would happen. Still only from was effected.

If anyone has any ideas what in the world could be going on with my bike and how to repair it that would be great.




Thanks,
Mike:motorcycl

it sounds like the float sticks but you say you have checked that....could it be vacuum related??

it sounds like the float sticks but you say you have checked that....could it be vacuum related??
I do not think there as a vacuum leak, but I guess it is possible. I have checked all the tubes to be sure they are free of holes and dry-rot and made sure they are all connected properly. Is there anything beyond that that I can do

Rember the front cylender is controled by the left carb. Some people have gotten them mixed up.
Have you checked the diaphram, could have a crack in it.

i'd check the diaphram.... keep in mind, that the amount of air/fuel is actually controled by the vacume, not the throttle in CV style carbs. All the throttle does is release pressure on the slide to allow the vacume to open it....also could be a stuck float.

Sounds like a stuck float. If you haven't already, try the Seafoam treatment. Seafoam can help in most situations like this. If not, you may need to tear the carbs apart again and go over the float assembly with a fine toothed comb. You didn't mention how many miles are on the bike but just to let you know, the float valves can wear a groove in them that prevents them from closing properly. If the rubber part of the valve has an indentation in it where it seats with the fuel feed, this may be your problem. Any small crud in this area will cause similar problems. It could be a small piece of silicon or something.

Well I have tried Seafoam again and after a full day of riding it has fouled up again. I think this next week I am going to tear the Carbs out again, as much as I don't want to. I will keep all of you posted as to my progress.

I have the same bike with the same problem and I was wondering if you ever figured out what the problem was.

Thanks:
Morenste

My 93 was doing this awhile back and I ended up taking the carbs off and going over them. I didn't find anything but upon reinstall, the problem was fixed. Although I didn't see anything, I blew out all the openings with low pressure compressed air.
Again, double check where the float valve seats with the fuel intake and check the valve for an indentation where the rubber meets the brass. If the rubber is indented, this will cause an improper seal and allow the float to flood causing the poor performing cylinder.

If the front cyl is running that rich, I'm going to suggest you check your petcock vacuum lines and make sure you're not leaking gas from the petcock through the vacuum line to the intake. If so, it will run rich as heck.

Good call on the leaking fuel petcock. I got my bike from my brother-inlaw because it would only idle on one cylinder. He had the carbs rebuilt and it still happened sometimes. I rode from AZ to IN and it would not idle while going over the mountains. It got a lot better down at sea level. I put up with the rough idle for several years untill last summer it started to leak from the petcock vent. Rebilt the petcock and instant fix. I had thought it was a leaking float valve but was reluctant to rebuild the carbs and didn't want to pay someone to do it. About $25.00 and less than an hour to fix.

Glad your bikes runnin' good now, JPD. :motorcycl

I wonder if M9e ever got his troubles straightened out? :confused:

Even a blind bird finds a worm once in a while! :motorcycl Glad you got it fixed and can enjoy riding and not fixin!

It is now much much later and I have finally found the problem that was causing the front cylinder to go out. I recently rebuilt the motor, well still doing it, and found that I was severely lacking oil to my front cams due to and oil line blockage and my cams and rocker arms up there were toast. I am pretty sure my problems were coming from here rather than the carbs. I will know 100% for sure by the end of the week when I fire it up for break in

You've been dealing with this for almost two years? (obviously some time off but still...) :drool:

You've got to have some serious patience, and determination. :smiley_th

Let us know how the break in goes.

I also had tried the swapping the coils to no avail. I then put in another ignition module, also no good. It ended up being the carbuerator.

Glad you got it up and running.