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I have '98 kawasaki vulcan that was running well until it sat for over 2 months. After sitting, it would not start up, and I found that the float had been stuck open in the carburetor. The engine was getting very flooded with gas, and after getting the float free in the carburetor, I changed the spark plugs and oil. When I tried to start the bike again, it would fire and sound alright for about 10 seconds, and then it would start to die. When I open the throttle, the engine starts to rev up, but then it will stop and go back towards the idle, before it dies. Each time I try to start it after it dies, it becomes harder to get the engine to fire. I think that the most likely cause of the problem is that the float level on one or both carbs became off when I was cleaning and freeing them up. I was just wondering if anyone else has had a similar problem, or if this sounds like the float levels on the carbs are uneven or off. Thanks for any help or advice.
 

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Have you checked the petcock? If the diaphragm has a hole in it fuel can flow into the vacuum port of the carb... or there could be insufficient fuel flow coming from the petcock.

Just a place to look at aside from the floats. The procedure to check and adjust the float level is in the manual... I found it a bit confusing at first but I re-read til I understood it well enough to do it and it was pretty easy.

Checking the petcock first is easier than taking out the carbs though.
 

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Ok, first, have you had the carbs off? If not, you may need to remove them, and give them a thorough cleaning. But I would try soaking them in Seafoam while still on the bike first. Use only Seafoam, NOT automotive carb cleaner.

What probably happened, is that in 2 months, all the gas evaporated from the float bowls through the vents, allowing the floats to drop all the way down. Since the vacuum operated petcock will not allow more gas to flow into the carbs without the engine running, they sat empty for some time, and the residue from the evaporated gas caused the floats to stick. It also probably partially plugged up the jets. I know for a fact that would happen in 2 months here in AZ. Had it happen to a number of dirt bikes.

Normally I would recommend removing the carbs, taking them apart, and giving everything a good cleaning, just so you know everything in there is ok. But the Vulcan 750 has the hardest carbs to remove of any bike I have ever owned, so trying something else may be worth trying first.

Put the bike on the centerstand, remove the fuel lines form the petcocks, loosen the carb float bowl drain screws and drain out all the gas. Now, using a very small funnel, fill the float bowls full of straight Seafoam through the fuel lines. Turn the engine over with the starter a few times. The engine should fire, though it may not actually run. Do that until smoke comes out the exhaust. Do it both with the throttle closed and completely open. The reason for doing that is to actually suck pure Seafoam up into the jets. Let it sit about 24 hours, drain out the Seafoam, and refill the carbs with gas, and start it up. If it is better, but still not quite right, ride the bike for awhile (if it is rideable) with Seafoam in the gas (you can pour a whole 16 oz can in a full tank of gas without problems) and see if it clears up. If not, it is worth going through the whole soaking procedure at least once more before pulling the carbs.
 
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