rear cylinder cold during warm up - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 29 (permalink) Old 03-15-2015, 05:07 PM Thread Starter
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rear cylinder cold during warm up

Not sure if this is the proper place for this but here goes

The bike a 2002 vn750, ear shaved,stock exhaust, supposed 7400 miles.

Ok so during warm up the rear pipe doesn't really get hot until really warmed up. So I know I have spark on one of the rears cause I took off the one on the left side in the tube and could feel it giving me a slight pulse and when I touched the engine I could see spark. Why I could feel it on the boot,could I need New wires? I'm pretty sure I'm getting fuel cause It smells rich during warm up.

Also the rear cylinder is just warm to the touch the first min or so but if I blip the throttle it revs a little higher for 10 15 secs and settles back down to 1100 rpm with full choke and it seems to kick in for a sec and I can feel more heat.

Once it's warm it seems fine hot to the touch after riding.



What you guys think?

Last edited by michiganrider1982; 03-15-2015 at 05:10 PM.
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post #2 of 29 (permalink) Old 03-16-2015, 06:19 AM Thread Starter
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Anyone?

It is what it is.
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post #3 of 29 (permalink) Old 03-16-2015, 08:57 AM
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Question

I'm curious about the spark.

It's not too unusual for a plug boot to leak voltage, and it's not a problem until a ground gets close enough, like where the throttle cables pass by the front plug.

The part about the spark giving you "a slight pulse" sounds like trouble, unless you are really resistant to electric shock, I would have jumped a mile if it were putting out good spark.

What color was the spark? Did it have a good snap when it hit or did it just sort of light up? Would it jump a wide gap, say about 1/2"?

Smelling fuel could mean the one cylinder isn't firing yet, or could be from having the choke on.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
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post #4 of 29 (permalink) Old 03-16-2015, 09:05 AM Thread Starter
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Gonna check the spark out more when I get home today

Wondering if the spark gets more intense with rpm or if it is the same all the time

It is what it is.
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post #5 of 29 (permalink) Old 03-16-2015, 09:39 AM
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Spark should be the same always. In some conditions you may see weak spark that picks up with rpm.

The spark should be blue, jump a wide gap like lightning, while giving off a 'snap'. If it's orange/yellow, maybe a bit fat, and sounds more like a tiny 'click', it's weak.

If you see weak spark, check the other wire too. It might help decide if it's the wire or the coil, etc..

Voltage to the coil is important, worth checking if the spark is weak. Then there's the coil relay mod, and the pickup coil mod.

I'm assuming the charge and battery voltage is good at startup?

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 #6 of 29 (permalink) Old 03-16-2015, 07:03 PM
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Sounds like a stuck float. Try this, start the bike and shut off the petcock, see if it starts to run normally. Until the bowls run out of gas that is...

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Last edited by shark88; 03-16-2015 at 07:14 PM.
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post #7 of 29 (permalink) Old 03-20-2015, 02:18 PM Thread Starter
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ok time to update I tested the spark plugs today all four have good spark.good blue sparkbut still having issues. so now I think it may be your carb problem. nNot not sure how to move this thread.


it's just strange how at idle the rear cylinder seems dead but as soon as I rev up to 1500 2000 rpm it just comes to life so any help is still appreciated. I am running the carbs with stock jets and the idle screws turned out two and a half in the front and three point five in the back.

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post #8 of 29 (permalink) Old 03-20-2015, 03:14 PM
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Are the rear plugs about the same color as the front? Black indicates a rich mix. White to light tan is lean.

In another direction, I wonder if it could be carb synch? On some bikes you can use a finger to open the throttle on just one carb, Like down where the cable hooks up. Maybe see if opening the carb slightly brings that cylinder to life.

Or slip the boots off the rear of both carbs, see if the butterflies are opening at the same time. Or, in the idle position, you may see that the rear carb butterfly is closed more than the front carb.

Last, maybe a dirty pilot jet or idle circuit.

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 29 (permalink) Old 03-20-2015, 03:40 PM Thread Starter
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Can I see that from the filter side of the carbs

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post #10 of 29 (permalink) Old 03-20-2015, 03:48 PM
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Yes, if you have pod filters, just take those off.

edit: On second thought, the slide might be in the way, but I think you could lift it up. Still may not see enough though.

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

Last edited by Spockster; 03-20-2015 at 03:50 PM.
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