Running on one cylinder - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 10 (permalink) Old 09-04-2010, 05:11 PM Thread Starter
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Running on one cylinder

I have a 2002 750 and I am having a problem of it only wanting to run on one cylinder. I checked all the spark plugs and wires they are all firing. The compression is also good on both cylinders. We have two of these bikes and when I take any of the spark plug wires loose on my dads bike the bike begins to run rough and if I take off two from the same cylinder it will still run but really rough. On my bike if I take off either of the back spark plugs the engine note does not change. I can even take off both plugs from the rear and it will still go unchanged. If I take off either of the front two the engine bogs down and almost shuts off. So the only thing I was thinking was that it could be the carb on the rear cylinder acting up. The part that amazes me is that the bike will still launch hard like it is running on both cylinders but I can take the wires off the rear and it will still run the same even going down the road. When I look at the spark plugs on the rear they have a yellowish tent to the tip of the spark plug while the ones on the front look normal and are white.
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post #2 of 10 (permalink) Old 09-04-2010, 07:54 PM
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How old are the plugs? Are they iridiums? Normal plug color is light tan.

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post #3 of 10 (permalink) Old 09-04-2010, 11:03 PM Thread Starter
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The plugs are not that old but why would it not react to removing of the wires on the back cylinder? And yes they are iridiums.
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post #4 of 10 (permalink) Old 09-05-2010, 10:38 AM
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Check the coil for the rear cylinder, sounds like a likely culprit.


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post #5 of 10 (permalink) Old 09-07-2010, 09:29 PM Thread Starter
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When the bike warms up you can hear a difference when you unplug one of the spark plugs but when it is cold nothing. The coil for the rear is putting out the same as the one for the front as far as I can tell the sparks are the same strength by using a spark tester. I was thinking that the coils might be getting weak but I thought when a coil got weak it got worse when the vehicle got hot not better. I was also thinking about doing the mod to where my coils ran off the battery to increase the voltage to them.
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post #6 of 10 (permalink) Old 09-29-2010, 08:45 AM
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Were you able to fix your problem. Mine is doing the same thing but the front one is not running.

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post #7 of 10 (permalink) Old 10-03-2010, 02:16 AM
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Does the cylinder start firing if you rev it to 2500 rpm or higher? If so then your pilot jet is likely plugged. Your main jet circuit kicks in at higher rpm and bypasses the idle circuit. You can remove your float bowl and carefully blow the jets out with compressed air (it can be done without removing the carbs). If that doesn't work, remove the carbs and clean them. The fuel petcock screen will still let fine dirt particles through that can plug the jets so you'll want install some small in line fuel filters.

If the cylinder doesn't light up when you rev and you have good spark (through your spark plugs), then you'll probably have yank the carbs and thoroughly go through them.

Hope this helps!

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post #8 of 10 (permalink) Old 10-03-2010, 08:42 AM
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You can check for spark by pulling off a wire and plugging in an old spark plug then ground it to the motor while its running. Or plug in a paper clip and hold it close to the motor ,spark should jump.
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post #9 of 10 (permalink) Old 10-04-2010, 07:49 PM
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Last edited by FlacoLove; 03-26-2013 at 12:36 PM.
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post #10 of 10 (permalink) Old 10-07-2010, 07:25 PM Thread Starter
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Ok my problem migrates from one cylinder to the other depending on if my bike is leaned over or sitting straight up as if you where riding it. When the bike is leaned over the back cylinder does not get gas. When the bike is sitting up as if you where riding it the front cylinder does not get gas. I just installed the Accel Super Coils on it and they helped a lot so I know my old coils where going bad but what would be causing the fuel problem? I was thinking the peacock but I was not sure. Both bikes are doing this by the way and part of the problem on the 93 is the cam tensioner is sticking and I am going to try and fix this soon but I do not think that is my main problem. This problem is happening equally in both the 02 and the 93 so the cam tensioner is responsible is not the problem but it is causing the 93 to back fire a bit at low rpms but the bike makes up for it at high rpms cause it evens out. Oh and at higher rpms both cyclinders run fine on both bikes it is just at low rpms. But like I said it migrates depending on if it is leaned over or not.
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