Help please problems at round 50mph - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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Where does this wire go?
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post #1 of 16 (permalink) Old 06-30-2018, 05:27 PM Thread Starter
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Unhappy Help please problems at round 50mph

Hello Vulcan collective,

I need help please, my vn700 is giving me much headache.

The float valves failed and hydro locked my bike, I changed the oil & filter and changed the float valves in the carbs, put it backed together & it was backfireing like a Gatling gun, so I synced the carbs & she ticks over nicely now but something isnít quite right, i can tell that the rear cylinder is missing the odd firing compared to the front ( I have straight pipes with screaming eagles baffles) you can feel it by the air out of the exhaust isnít quite right , if I rev the bike I can reach 7-8krpm no problem but as soon as I ride it down the road I canít get above
45-50mph at 4-5krpm she just stops reving splutters and dies.
Iíve tried everything I can think off.
Please can some wise Vulcan owner point me in the right direction.
Many thanks peter

Ps I hope this makes sense.
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post #2 of 16 (permalink) Old 06-30-2018, 05:53 PM
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Just repeating what I've heard here as have not had this problem myself, but word is that the gas in oil problem is more likely due to a failed petcock than failed float valve. Apparently when the petcock fails gasoline will flood the vacuum lines and go straight into the engine without ever going through the carbs at all!

Maybe a petcock problem is causing your trouble? Would be easy enough to pull your vacuum line and see if gas is running out of it. . . .

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Last edited by GDI; 06-30-2018 at 05:54 PM. Reason: suggested a diagnostic technique
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post #3 of 16 (permalink) Old 06-30-2018, 06:04 PM Thread Starter
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Hi GDI,

Many thanks for your reply, should of mentioned but forget, I replaced the petcock for good measure as well, also when syncing the carbs no fuel was coming out of the vac lines.
Thanks for that tho.

Last edited by ateam; 06-30-2018 at 06:09 PM.
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post #4 of 16 (permalink) Old 06-30-2018, 06:28 PM
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What type of battery? AGM?

How well does it start? Backfires on startup?

Sounds a lot like what I'm chasing, but mine clears up when the voltage goes back to normal.

https://www.vn750.com/forum/19-electr...problem-3.html

Have you checked the charging voltage?

Going the other way - Have you checked the slide diaphragms really close?

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 #5 of 16 (permalink) Old 06-30-2018, 06:42 PM Thread Starter
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Hi spockster,

Thanks for your reply, I have just put a brand new gel battery on her as they produce a higher current output than lead acid.
I will have to check tomorrow what the voltage is, but she starts up fine with no backfires and ticked over ok.
Hence Iím scratching my head, i put aftermarket coils on her and Iím wondering if they are not man enough under load?
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post #6 of 16 (permalink) Old 06-30-2018, 06:52 PM
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Check the spark with a screwdriver in the plug boot, if it's a nice bright blue and will jump a 25-40mm gap, it should be fine. Watched mine in the dark last night and at least one plug boot is arcing to the head.

If it's yellow/orange and doesn't have a good *snap*, just acts kinda slow, lazy, and just lights up, that's no good.

Back to those diaphragms ... It's good to flex them around in front of sunlight, or other bright light, to check for cracks. Can do a lift test on the slides and see how they react. If the slide just flops back down, the diaphragm is leaking. Should drop back down with some resistance and you should hear air wooshing in the carb.

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 #7 of 16 (permalink) Old 07-01-2018, 11:29 AM Thread Starter
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Quote:
Originally Posted by Spockster View Post
Check the spark with a screwdriver in the plug boot, if it's a nice bright blue and will jump a 25-40mm gap, it should be fine. Watched mine in the dark last night and at least one plug boot is arcing to the head.

If it's yellow/orange and doesn't have a good *snap*, just acts kinda slow, lazy, and just lights up, that's no good.

Back to those diaphragms ... It's good to flex them around in front of sunlight, or other bright light, to check for cracks. Can do a lift test on the slides and see how they react. If the slide just flops back down, the diaphragm is leaking. Should drop back down with some resistance and you should hear air wooshing in the carb.
Hi Spockster,

I checked my spark itís nice and blue, also checked what the charge is at tick over Iím getting 13.9 volts if I rev her it goes up to 14.2 volts.
The diaphragms look good as well any over suggestions welcomed
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post #8 of 16 (permalink) Old 07-01-2018, 12:00 PM
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Hmm, running out of ideas.

It reads like insufficient fuel flow, either dirty jets or restricted flow from the tank. It takes a lot less fuel to rev on redline in neutral, than it does just to cruise along at 3000 rpm.

Barring that, ignition falling off at that point? I still lean toward fuel. Clean the carbs again?

When it "sputters and dies", is it shutting down completely or does it come back when you let off the throttle?

I don't think it's POOGS, since it seems to do this right away when you try to ride.

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 #9 of 16 (permalink) Old 07-01-2018, 01:44 PM
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is it ear shaved?? (I just skimmed the posts) of so, check carb vent routing
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post #10 of 16 (permalink) Old 07-01-2018, 02:01 PM
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Quote:
Originally Posted by michiganteddybear View Post
is it ear shaved?? (I just skimmed the posts) of so, check carb vent routing
Damn good question, forgot all about that.

Even if not earshaved, are the vents routed correctly?

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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