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master of reality
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Discussion Starter #1 (Edited)
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?
 

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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.
 

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master of reality
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Discussion Starter #4
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
 

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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?
 

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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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master of reality
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Discussion Starter #7
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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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.
 

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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.
 

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master of reality
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Discussion Starter #11
Yes the plugs are light tan all 4...just started it col and was missing like normal but I tried something I leaned the bike hard to the right and the rear sputtered to life also turned the air mixture screw all the way in and let it run then backed it out 1.5 2 turns.


Another thing I noticed was my batt is bad been boiling over but I got 12.6 cold and with the bike running I got like 17.2volts and after I killed it it slowly droppeduntiligot tired of waiting......is my regulator bad? Could that also be screwing with my rear cylinder?
 

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When you leaned the bike, did you also turn the bars? Sometimes the cables will pull a bit when the bars are turned one way. Otherwise, it might indicate a float level problem.

17v is a pretty hot charge, and why the battery is boiling. Could be trouble in the r/r, but shouldn't kill the one cylinder. Make sure the batt. terminals are tight and clean.
 

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That could tip the fuel in the bowl and make it behave like it has a higher float setting. Seems like it might not be getting fuel into the idle circuit.
 

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Would need to check the float level. Some here have done it with the carb in place, but I haven't done it yet. Maybe try the search or look through posts made by wmsonta , he's a pretty good carb man. Or maybe someone will chime in.
 

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master of reality
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Discussion Starter #17
Ok update played with it some today pulled plugs after warm-up and they are fouled and wet Mabey fouled from idling so much but they were wet.... So I cleaned them up 're gapped to .035 and went for a ride,pulled the plug and it was light tan white but I turned the air fuel screw all the way in and back out 1.5 turns before the ride
So my thought is that in getting gas just no fire at idle.
Seemed to have ok blue spark at idle so I'm confused.
 

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Still sounds like it is flooding. Turn off you gas petcock and try starting it and see if the cylinder starts firing up as the float bowl starts to drain. That will tell you if you're flooding. You'll know in about a minute if that's the problem.
 

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FREEBIRDS MC CENTRAL NY
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X2 on what shark said
 

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The rectifier is putting out over 15 volts so it is defective. The battery is probably toast also. These have to be corrected first before solving the problem.
 
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