Bad fuel valve? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 08-17-2011, 01:36 PM Thread Starter
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Bad fuel valve?

I just got a call from Carbworx. Steve said my carbs looked good and only found that they had the incorrect main jets in them. I'm not sure that addresses all my issues though. What I'm seeing is

1) Very inconsistent idle. Sometimes I'll come to a stop sign and get 1500 RPM, sometimes 800, sometimes 400 and sometimes it won't idle.
2) If I run the throttle open for a bit just standing I'll blow black smoke and then it will idle ok for a couple seconds
3) I can't take the choke off when the bike is running. It sounds odd but even once its warmed up taking the choke off will kill the engine. So I take the choke off, then restart and it fires up and runs fine.
4) I can't add any throttle with the choke on. Cold or warm if I increase the throttle at all the bike will die.

So Steve suggested I might have a bad fuel valve. Anyone seen this before? I've thought about perhaps replacing the valve with one that has a "prime" position so I can discount issues with the vacuum diaphragm. Suggestions??

-Robert
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post #2 of 7 (permalink) Old 08-17-2011, 03:45 PM
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If you are going to switch petcocks, why not just go for a gravity fed model? Someone posted one that would fit the Vulcan.

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
_____________________________________________
"Black Beauty"
1989 VN750 acquired December, 2008, 6,711 miles
Currently 23,298 miles

Old Blue
2001 Honda CMX250 Rebel acquired July, 2008

1987 VN750 project bike, acquired August, 2009, 33,000 miles and balancer sticking out of the case, currently awaiting attention and parts
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post #3 of 7 (permalink) Old 08-17-2011, 04:30 PM
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IIRC it was a Yamaha product -- part# 23F-24500-11-00. They were about $12-13 at cheapcycleparts.com compared to about $57 for a new Kaw OEM petcock.

Hope this helps.

John

1989 VN750
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I'm bad with names. May I just call you dumb?
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post #4 of 7 (permalink) Old 08-17-2011, 06:52 PM Thread Starter
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As an aside, I've noticed that I can idle the engine with the valve in the "off" position. It doesn't idle as smooth but it won't die. Is this normal or another indication of a bad petcock?

-Robert
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post #5 of 7 (permalink) Old 08-18-2011, 07:57 AM
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If you can do it long enough to burn all the gas in the carb, I would say the petcock is leaking.

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
_____________________________________________
"Black Beauty"
1989 VN750 acquired December, 2008, 6,711 miles
Currently 23,298 miles

Old Blue
2001 Honda CMX250 Rebel acquired July, 2008

1987 VN750 project bike, acquired August, 2009, 33,000 miles and balancer sticking out of the case, currently awaiting attention and parts
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post #6 of 7 (permalink) Old 08-18-2011, 08:55 AM
If only it had 6th gear..
 
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Quote:
Originally Posted by johnm View Post
IIRC it was a Yamaha product -- part# 23F-24500-11-00. They were about $12-13 at cheapcycleparts.com compared to about $57 for a new Kaw OEM petcock.

Hope this helps.

John
Knifemaker had posted that the vavle really wasn't a good alternative for our bikes. I can't look up that number right now b/c I'm using the phone but if its the single outlet valve you might want to ask him just in case. Someone else however, used a single outlet successfully so maybe it would be fine. Just throwing it out there for the info. Please chime in any who have used them as I may buy one next season since its cheaper than rebuilding mine . Ride safe guys.
dt
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post #7 of 7 (permalink) Old 08-18-2011, 12:19 PM
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Strange symptoms indeed.

Check throttle cable adjustment. Both throttle cables must not be tight at the same time. This could cause your inconsistent idle.

Check that the choke plunger really completely closes when you take the choke off (push the plunger with a finger and see if it moves).

Your main jet size does not affect the idle. A leaking petcock does not cause problems if the float valves work. If the petcock does not open properly that would cause problems. I suspect the float valve(s) leak. Try to set up a gravity feed for the carbs and see what happens.
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