One last try before bringing it into the garage - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 07-31-2019, 07:45 AM Thread Starter
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One last try before bringing it into the garage

Hello guys,

It’s been a while since I made a post about what is wrong with my bike. Since I have no idea what is wrong with it and how to fix it this will be my last post on this problem before I am bringing it in to the garage and have an mechanic look at it.

So the problem started a month or so ago. The RPM gage just won’t stop going up and down when in idle and when throttling/driving. It’s almost impossible to drive the bike without it being at 4k to 5/6k rpm. Since im not good at explaining what the problem is I made a video earlier showing the problem. Note that this was in the early stages of the problem and its since does this at all rpm ranges.


After This I checked all the vacuum tubes of the bike. I checked the Carb Boots and the diaphragm, removed the entire carb and opened it up Nothing looked out of the ordinary except for fuel in the picture added this is the right side of the carb.



I also used a repair kit on the petcock.

After a while I noticed the bike would run nicely (sometimes if it’s on the side stand). See video.

Can anyone help me with this? I have heard a lot of you say it might be a vacuum problem. Is there any way i can check for this?

I have no idea what to do. And i might bring it to a garage to get it fixed as a last resort.

Last edited by Panarock; 07-31-2019 at 07:47 AM.
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post #2 of 9 (permalink) Old 07-31-2019, 08:49 AM
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I think I remember this thread, if it’s a vacuum issue, you can spray the carb boots/connections etc with WD-40 while the bike is running. The point is that if there are holes or cracks in the assembly the WD-40 will get sucked into the whole and it will cause the engine to stumble. My bike did the same thing once but it was because the hose clamp got the boot came loose from vibration causing it to suck in way too much air. If you’ve already done this because somebody else mentioned it then sorry for the repeat advice.
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post #3 of 9 (permalink) Old 07-31-2019, 09:47 AM
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My guess is if it's not an airleak on one of the intake boots somewhere it might be a hole or tear in the rubber diaphragm that controls the slide in one of the carburetors.
This would cause erratic engine speeds even when the throttle is held still.

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post #4 of 9 (permalink) Old 08-01-2019, 11:17 AM
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Think I recall from the other thread ... Carb boots have tested more than once, diaphragms look like new, carbs have been cleaned, etc.

Thinking about the running symptoms, it looks like something I've seen 2-stroke dirt bikes with a bad plug, not exactly a fouled plug but a plug with maybe a resistance problem. I'm wondering if this has anything to do with the resistors in the spark plug boots on the VN750? Or possibly the CDI unit? I recall some discussion about the resistors, but not specifics. I know Wolfie said he removed the resistors from his boots, but don't recall what the exact problem was.

What color is the spark? Blue/white with a good snap to it, like lightning? Or yellow/orange and just lights up, but a lot slower/weaker than lightning?

I'm betting you've changed plugs ... Do you have the old plugs you can try in it?

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post #5 of 9 (permalink) Old 08-01-2019, 06:31 PM
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I dug up an old thread about the plug cap resistors. Now i'm thinking if the resistors were a problem, you might have no spark at all.

But it does seem like your ignition could be breaking up as soon as the rpm is raised.

So that still points to the need to observe the spark. I would check one wire at a time, noting the strength, consistency, and color. I did mention this in your other thread, but not sure if you checked.

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post #6 of 9 (permalink) Old 08-03-2019, 01:29 PM Thread Starter
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Quote:
Originally Posted by Spockster View Post
I dug up an old thread about the plug cap resistors. Now i'm thinking if the resistors were a problem, you might have no spark at all.

But it does seem like your ignition could be breaking up as soon as the rpm is raised.

So that still points to the need to observe the spark. I would check one wire at a time, noting the strength, consistency, and color. I did mention this in your other thread, but not sure if you checked.
I did change the sparkplugs 8 months ago. I switched back to them and tried to start. it had the same problems, I didnt check how the spark looked yet. but the fuel was gone so it didnt start, after a while the negative charge of the battery melted off. (after 1 min of trying to start) This must be an indication that something is wrong electrically
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post #7 of 9 (permalink) Old 08-09-2019, 02:57 PM
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I had a very similar issue a few years back. My tach was all over the place. Finally the front (if i remember correctly) cylinder quit during a ride in the rain. I spent a month tracking the problem down to a ground in the wiring harness lead to the coil for that cylinder. The tach also runs off this coil hence the weird needle bounce. Instead of tracing out the issue in the wiring harness. I ran a separate lead and spliced it in from that coil to the igniter. One other peculiar electrical issue (before the coil) I had was when I turned the handle bars to the right with the bike running, so I could hop off to open my garage the bike would shut off. It always restarted. The issue hear was the wiring harness connection was loose at the junction point under the gas tank. When I turned the handle bars it would pull slightly on the harness and cause an open at the connector. I cleaned the connector up and made sure it snapped together securely and all is well again.

Last edited by groundzero879; 08-09-2019 at 03:04 PM.
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post #8 of 9 (permalink) Old 08-26-2019, 05:33 PM
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I would agree that its something electrical. The thing about that is its a pain tracking down exactly what it is. Theres a video on YouTube where this guy takes out his whole wiring harness and lays it out. Gets new wire the same colors as the bike has originally and makes a new harness himself. Thats always a option and much cheaper than buying a new harness online. Just take a little while making it. But if you was to do that you want to make sure you clean up every ground connection where its grounding to the bike.
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post #9 of 9 (permalink) Old 08-27-2019, 03:23 PM
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Quote:
Originally Posted by Rollerzonly View Post
I would agree that its something electrical. The thing about that is its a pain tracking down exactly what it is. Theres a video on YouTube where this guy takes out his whole wiring harness and lays it out. Gets new wire the same colors as the bike has originally and makes a new harness himself. Thats always a option and much cheaper than buying a new harness online. Just take a little while making it. But if you was to do that you want to make sure you clean up every ground connection where its grounding to the bike.
These harnesses are like a big bowl of sghetti

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