Falling flat on itís face - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Unread 02-02-2020, 06:30 PM Thread Starter
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Falling flat on itís face

Got myself an issue. See the video. Basically it falls on it’s face above 4k.




front plugs were wet so i thought maybe a coil was failing, but after cleaning them the haven't been wet since so idk. I have fuel in the carbs. Voltage of the bike is great. I have all the mods done.


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post #2 of 8 (permalink) Unread 02-02-2020, 09:15 PM
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I've never been able to play a video posted on this site. It always says an error has occurred.

So, without seeing/hearing the video: Perhaps pull the main jets and clean them well. They can be reached while the carbs are still installed. 4K is about the rpm where they would kick in. If they're clogged it would run fine below 4K but crap at and above 4K.
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post #3 of 8 (permalink) Unread 02-08-2020, 04:10 AM Thread Starter
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I agree. What threw me off was the wet plugs in the front cyl, but I haven’t seen them wet since so I’m working on it from fuel for now. When i drained the carbs to pull the main jets today the front cyl was low on fuel in the bottom of the bowl. Probably 1/2 what it should have. I didn't Have any clogged jets as best i can see, so if it’s still acting up tomorrow when i finish putting it back together and i see low fuel volume in that carb I’m going to have to pull them and check the float system.


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2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

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post #4 of 8 (permalink) Unread 02-09-2020, 12:18 AM
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I can't see the video either. But if you mean the engine cuts out above 4,000 RPM, it is almost certainly a carburetor issue. If you have pod filters and a gutted exhaust, it could simply be too lean.

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post #5 of 8 (permalink) Unread 02-17-2020, 05:10 PM Thread Starter
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Rebuilt the carbs. No change. Time to swap coils and see what it does.


1981 KZ750
1988 Vulcan VN750 (red)
2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

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post #6 of 8 (permalink) Unread Yesterday, 01:39 PM Thread Starter
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Coil swap did nothing. Very odd issue.


1981 KZ750
1988 Vulcan VN750 (red)
2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

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post #7 of 8 (permalink) Unread Yesterday, 03:23 PM
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Possible fuel flow issue? (If float bowl is only half full)

Crack in vacuum line, clogged fuel line or petcock?

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post #8 of 8 (permalink) Unread Today, 12:56 PM Thread Starter
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I changed the diaphragms on the coaster area and they were moving. Since it cuts both cyl now i have to assume it’s before the carbs. When it first started only 1 cyl sounded like it was cutting. Now both cut completely off when i twist the throttle. It will idle all day long and run fine at partial throttle, which makes it very hard to figure out since it has everything it needs to run just not enough of something. Voltage is very strong though. That Ricks stator is awesome and is driving nails. I may need to check the VR output on each pin just for kicks, but at the battery it’s regulating at 14v strong.

When it first started i felt like it could be a clogged carb. It acted like it was running out of gas with one cyl cutting out. I eliminated poogs by opening the gas cap lid. Then the next day it ran great for a day, then both cyls cut out from then on.

Since i have the coil mod I’m going to check the relays output, but i don’t think anything is going on with it. It’s clean as new inside.

First thing though is to swap the brain box from a stock VN i have to this one and see what happens. I think between all my mods I’ve mostly bypassed the fuse box, but just to be sure. I’ve bypassed the headlight, relay on the coils, shaved pickups, and everything else.

Oh and there is something I can’t see in the manual which is in black and white..... which color goes on which coil for the rear ign coil? I can’t tell with my bikes because i have new wiring on them. It appears as though green is on top.


1981 KZ750
1988 Vulcan VN750 (red)
2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

Engineering solutions for the VN750 Community.

Last edited by One1; Today at 01:10 PM.
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