Running issues - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 27 (permalink) Old 05-30-2013, 09:29 PM Thread Starter
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Running issues

I have a 2002 Vulcan 750. No modifications.

I've been having some running issues lately.

The engine runs well at idle. No issues there. Starts well, hot or cold. The problem is, I've noticed that the slow speed engine torque is way down and when I start from a stop, I have to rev the engine a lot more than I should in order to start from a stop without stalling. The engine sounds almost like it's running on only one cylinder from 1000 rpm up to about 3000 rpm. Once it hits 3000 rpm, it runs fine.

The second issue is that sometimes, when I've been riding it for awhile when I come to a stop, the engine rpms will stay high...around 3000 rpm. If I let the clutch out a bit to drag the engine down, the rpms drop to normal. If I don't let the clutch out, it may or may not drop the rpms down.


I've checked the throttle linkage and it's moving within the full range.

I pulled the float bowls off (not sure if that's the right term but it's the part that is held on by two screws and holds fuel and also accesses the fuel jets) and checked it. There was a tiny bit of sediment in the bowl but nothing bad. Looked very clean.

So, any ideas?

I've ordered a rebuild kit for the petcock. I've been getting some seeping from the petcock so I'm sure it needs new parts inside. Not sure if it could cause the issues that I'm having or not.

Thanks for the help.
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post #2 of 27 (permalink) Old 05-30-2013, 10:25 PM
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Since you found some dirt in the cover under the jets try removing and cleaning the jets and emulsion tube. You may have a lot of junk blocking some of the fine holes in them.

As far as the high warm idol there are several things that could cause that. Sticky throttle cable (spray some lube on cable and carb linkages) or maybe a sticky or improperly fastened choke linkage to the carbs could also keep the choke from fully releasing. Bottom line is it may be time to just rebuild the carbs. They can be a chore to get in and out but rebuilding them is pretty easy.

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post #3 of 27 (permalink) Old 05-30-2013, 11:06 PM
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Sounds like you have a clogged pilot jet or both are clogged. The bike runs off the pilot jets until about 2500 rpms and then the main jets kick it. I would adjust your accelerator and decelerator cables to try to steady your rpms at idle. I had to do mine today to correct the problem that started yesterday.

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post #4 of 27 (permalink) Old 05-31-2013, 12:57 AM
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Yes, the petcock could leak gas to one cylinder only and cause a lack of power at low rpm's. You could pull the center vacuum line off the petcock and look for evidence of gas. Or hook a mityvac to it and see if gas enters the hose.

If gas leaks into that hose it goes straight into the cylinder not the float bowl.
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post #5 of 27 (permalink) Old 05-31-2013, 08:50 AM Thread Starter
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Quote:
Originally Posted by wmsonta View Post
Yes, the petcock could leak gas to one cylinder only and cause a lack of power at low rpm's. You could pull the center vacuum line off the petcock and look for evidence of gas. Or hook a mityvac to it and see if gas enters the hose.

If gas leaks into that hose it goes straight into the cylinder not the float bowl.


Thanks for all the replies so quickly!!

I pulled the vacuum line off and checked it. There was some evidence of liquid fuel in the vacuum line so I'm pretty sure that the petcock needs to be rebuilt. I did try to apply vacuum with a vacuum pump but was unable to get fuel to come out the vacuum line. But, there was liquid fuel in the vacuum line so there definitely is some fuel leaking past the petcock and into the cylinder at least occasionally.

Parts are on order for it.

As far as the throttle linkage, it works smoothly and is within the full range of motion. On one of the times that the bike was idling too high, I reached under the tank to the carbs and manually grabbed the linkage to try to force it closed. It was fully closed but the idle was still too high. Messing with the linkage didn't change anything. Dragging the motor down with the clutch drops it right back into the normal RPM range.
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post #6 of 27 (permalink) Old 05-31-2013, 10:56 AM
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I had similiar issues months ago. I pulled the carbs and cleaned, rejetted to 142/42's with 2 shims each needle. Earshave, Pods and coastering solved my ills. Runs great ever since. No regrets.


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post #7 of 27 (permalink) Old 05-31-2013, 03:35 PM
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I had the same problem when I first got my bike.... I had crud in the actual petcock... try taking it apart and see if its dirty.

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post #8 of 27 (permalink) Old 06-02-2013, 11:12 PM Thread Starter
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Thanks to all for the info. I'll have the parts to repair the petcock early this week so I'll clean and rebuild it and we'll see what happens. I'll report back when I get it replaced.
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post #9 of 27 (permalink) Old 06-03-2013, 11:15 PM Thread Starter
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I got it replaced today. There was a little grit in the petcock but not bad. It seems to run better but I have to run it for a longer time to see if it actually repaired it. We'll see.
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post #10 of 27 (permalink) Old 06-03-2013, 11:23 PM
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I had trouble with mine, that I sold last wk. Seens I had used fuel treatment during winter, I cleaned the carb just by removing the jet bowl cover. I removed the jets blew them out and sprayed carb cleaner into all the holes. Blew air into the carb and air passeges. That fixed my problem. I did not remove carbs.

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