advice requested: no vacuum in rear carburetor ? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 4 (permalink) Old 09-06-2009, 04:56 PM Thread Starter
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advice requested: no vacuum in rear carburetor ?

So I have the bike running again but not as good as I had hoped to. Two issues I'd like your opinion on:

1. The rear carburetor doesn't seem to hold it's vacuum. Whereas the fuel line of the front carburetor is filled with no air, the rear carburetor fuel line has a lot of air in it. This doesn't change - it's there before and after the ride. Could this be a vacuum issue, maybe a hole in the diaphragm ? Or something else ?

2. The cooling doesn't seem to be ok. After the ride, the coolant was boiling and some of it spilled through the overflow line. The fan seems to function ok. Note: I had to substitute the radiator cap by a different one. This one has an 11 psi pressure limit (the original one 14 psi). Could this have something to do with it ?

Thanks for your opinion, I'm trying to figure it out here.
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post #2 of 4 (permalink) Old 09-06-2009, 08:32 PM
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Easy one on the radiator cap - you need the 14 psi. You should be able to find one at your local auto parts dealer, no problem.

For the carbs - kinda confusing, since you shouldn't have air in your fuel lines at all, but it does sound like your rear carb isn't drawing in fuel. If you pull the boot (carb to airbox) off the rear carb, and push up on the piston, you should hear a "skooosh" sound and feel a bit of resistance (not a lot, but some). If that piston just moves up and down easily, you may have a problem with the diaphragm - either a hole, or it's just not sitting right in the carb body. Have you cleaned the carbs lately? Or do you know when they were last cleaned?

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post #3 of 4 (permalink) Old 09-06-2009, 09:36 PM
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check the rear jug compression. It may be your valves are too tight.

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post #4 of 4 (permalink) Old 09-06-2009, 09:52 PM
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You will have an air pocket in the fuel lines, because they are fed buy gravity and not vacuum.

Since the fuel lines share the same petcock the air pocket from one will travel to the highest line. It will not cause any performance problems.


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Last edited by lance328; 09-06-2009 at 11:21 PM.
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