vacuum leak or fuel problem??? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 13 (permalink) Old 07-27-2012, 01:46 PM Thread Starter
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vacuum leak or fuel problem???

2005 vulcan vn 750; moved tank to install new coolant hose. 2 hoses apparently disconnected; (1) is from underseat emmissions-not sure where this connects. The other appears to be from (R) of left side carb, could someone explain where these connect??? Bike was running fine before moving gas tank, now will not start. Siphoned tank before moving and replaced some fuel, tank still unbolted and (R) side air-cleaner is removed... What could possibly be the problem? Bike cranks over fine; however acts like not getting fuel. Would apprecite any advice.... Thanks
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post #2 of 13 (permalink) Old 07-27-2012, 01:51 PM
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petcock is vacuum controlled.

vacuum hose from left carb goes to petcock. fuel will not flow unless vacuum is present. The center hole on the petcock is the vaccum line in question.
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post #3 of 13 (permalink) Old 03-21-2020, 12:10 PM
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2003 750 vulcan i put a new carb and petcock all vacuum lines good and hooked up correctly. idles great i warm it up before i drive it about a 1/4 mile and starts bogging down. Throttle hard on it seems to get better but normal throttle it bogs in and out. get back to shop and the front vacuum on petcock has some fuel in it. Anyone have any idea the problem. thanks
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post #4 of 13 (permalink) Old 03-21-2020, 03:27 PM
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Originally Posted by gravydave View Post
2003 750 vulcan i put a new carb and petcock all vacuum lines good and hooked up correctly. idles great i warm it up before i drive it about a 1/4 mile and starts bogging down. Throttle hard on it seems to get better but normal throttle it bogs in and out. get back to shop and the front vacuum on petcock has some fuel in it. Anyone have any idea the problem. thanks
If it's hooked up correctly, the petcock is bad. Should never be fuel in the vacuum line. This will also dump fuel into the oil.

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post #5 of 13 (permalink) Old 03-21-2020, 04:04 PM
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ok thanks for the imformation to bad oem petcock is bad.
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post #6 of 13 (permalink) Old 03-21-2020, 07:36 PM
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the front vacuum on petcock has some fuel in it. Anyone have any idea the problem. thanks
That’s not going to cause your bike to run poorly. Out of my 6 VN’s almost all of mine do it. Never had any issues. Most people run the factory black line to the petcock so they don’t know there is always some very light moisture in there. Only people that run clear tubes like I do know and see that there is always light moisture in the vac line.

Here’s you a video.



You need to check your snorkels at the carb. The back of them fold in when you put them on and don’t go all the way around the carb tight. Run your finger around the snorkel at the carb throat and the back side will probably be unseated and that’s what the bike will act like lean when that happens.


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Last edited by One1; 03-21-2020 at 07:42 PM.
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post #7 of 13 (permalink) Old 03-21-2020, 07:50 PM
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It can dump enough fuel to overfill the crankcase with gas and oil, not normal.

Un-metered fuel dumped into the intake can't help performance.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #8 of 13 (permalink) Old 03-21-2020, 08:08 PM
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thank you i will check it out
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post #9 of 13 (permalink) Old 03-21-2020, 09:50 PM
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does the fuel gas sending unit cover cap hose under gas tank hook to anything. I saw there is no hose on it
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post #10 of 13 (permalink) Old 03-21-2020, 10:11 PM
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Originally Posted by gravydave View Post
does the fuel gas sending unit cover cap hose under gas tank hook to anything. I saw there is no hose on it

No it doesn't normally have a hose on it.

When we do the earshave, it makes a good spot to connect the carb vents to keep them out of the wind, the wind pressure keeps the carb bowls from filling.

Maybe that nipple is on the cover to direct a fuel leak in a certain direction, or it's leftover from some other design and they just went with it instead of redesigning it.

Is your bike earshaved? If so, where are the carb vents connected? Wind on the vents does cause bogging.

If your air intake is stock, the carb vent hose that runs to one of the filter housings should have the end cut at 45 to prevent it sealing against the back of the filter housing. A clogged vent can cause bogging as well.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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