Rear Cylinder not firing under 4-5k RPM - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 09-15-2016, 12:55 PM Thread Starter
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Rear Cylinder not firing under 4-5k RPM

After all I've done to the bike, my battery is still dying after nearly 15 miles. Just bought a new lithium battery for out the a** at Advanced Auto Parts with a 1-year warranty, and didn't make it 1 mile shy of the ride home. I thought the bike was running fine after running some seafoam through it a couple times after the rebuild with tuxedo mod and caltric stator&R/R. But I recently dropped the bike gently at a full stop, enough to make it stall out. No damaged caused to the exterior of the bike surprisingly. But after that, it seems the rear cylinder isn't firing except upon acceleration past 4000 RPM, and then once RPMs are maintained it ceases to contribute and slowly bogs the bike down. And once the rear cylinder is firing, the bike will try to idle at only 4000 RPM regardless of throttle position until the rear cylinder stops firing, then bogs down until I gas it. I had a little bit of the exccessive RPM idle when running seafoam before, but it went away after one tank of treatment. The bike won't hold an idle anymore after I dropped it.

I'm dumb founded at what the causes of these problems could be causing this problems. I sure hope it's not the stator gone bad already, but I haven't been around the tools to diagnose that one recently. But I wasn't having these kinds of issues before with a bad stator, so... Only other idea would be pick-up coils got damaged some how like with another members results with his tuxedo mod. It also looks like I'm leaking gas somewhere from the petcock and choke ports on the carbs. Idk if that's just the Seafoam, but I'm 100% not looking forward to a potential petcock and/or carb clean and rebuild. I don't see how a slow lean over would cause this.

Has anyone experienced this and have a remedy for it? I'm gonna do the pick-up coil relay mod and clearance adjustment today if I can get the day off, that'll give me the chance to see what the stator's all looking like. I also may have a short somewhere, but I can't seem to find where. Everything looks solid and clean. It's only a 10 year old bike with low miles and was garage kept most of it's life.

2006 VN750A
Purchased in August 2015 with 8,500 miles, currently at around 15,000 miles
Once earshaved, but recently reinstalled a modified surgetank and airboxes(like the sound and look better)
K&N air filters
Jetted
Coastered
Vance & Hines Cruizer Pipes
Tuxedo mod
Blue-wire, Two-wire, and sidestand-switch modded
NGK Iridium plugs
New lithium constantly hooked up to a battery tender
Possibly dead, but brand new Caltric stator and R/R
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post #2 of 8 (permalink) Old 09-15-2016, 04:49 PM
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Which side hit the ground?

First step I'd take would be to narrow it down to electrical or fuel delivery. Could you have broken or dislodged a spark plug wire? Are you getting spark on the rear cylinder?

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post #3 of 8 (permalink) Old 09-15-2016, 08:54 PM
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You could have cracked/damaged a spark plug wire or spark plug itself. Check these first since they are easy. Then check to see if you have spark, you should be able to do this with a simple test light or by grounding out a spark plug. If you've got spark on both cylinders, then its not your pickup coils.


If that's not the answer, I agree that you need to figure out whether the problem is electrical or fuel delivery. My guess is that it is fuel related. It could be as simple as liquid (gas or otherwise) is plugging up an air vacuum line. Start by draining the fuel out of your carbs (should not require removal) and then disconnect the vacuum lines and make sure they are free flowing. Blow a little compressed air around the area. See if that helps you out.

Once you figure out the cylinder firing issue, get a basic multimeter and check the voltage at the battery with the engine running and report the results.
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post #4 of 8 (permalink) Old 09-16-2016, 09:05 AM Thread Starter
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Bought a new lithium battery from AGM and ultimately disappointed with it. Works worse for me so far than the cheapo AGM battery I bought from Walmart, even though it has far more cold cranking cranking amps. Might have to return it....

I'll check the spark plugs, but I hope it's not them because I just replaced them XD.

It was the left side that fell. Gas tank, turn signals or pipes didn't even touch the ground. Just the center stand and handlebars.

Worst case scenario, I'm thinking the new caltric stator was some how damaged by it. But I don't understand how this would stop the rear cylinder from firing under 4000 RPM and keep the front cylinder struggling. I'm gonna stop riding it for now, since it's stuck at Walmart currently, and start taking the miserable and expensive bus route again and work on some mods a few weeks from now when I have a weekend off.

Can anyone put me in touch with TPE for a rewind?

2006 VN750A
Purchased in August 2015 with 8,500 miles, currently at around 15,000 miles
Once earshaved, but recently reinstalled a modified surgetank and airboxes(like the sound and look better)
K&N air filters
Jetted
Coastered
Vance & Hines Cruizer Pipes
Tuxedo mod
Blue-wire, Two-wire, and sidestand-switch modded
NGK Iridium plugs
New lithium constantly hooked up to a battery tender
Possibly dead, but brand new Caltric stator and R/R
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post #5 of 8 (permalink) Old 09-16-2016, 09:51 AM
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I know some people like TPE stators, but the one I bought from him only lasted 1 year before it also died, and then he quit responding to my emails inquiries about buying a 2nd one. So I guess he doesn't want my business anymore. Anyway, I bought a Rick's Motorsports Stator and so far so good. (DennisKirk.com)

I personally wouldn't buy an expensive part like a stator until you confirm its bad, which means testing it with a multimeter with a properly running engine. It could be as simple as one of the stator wires was disconnected near the centerstand area when the tip over happened.


It could be as simple as a stuck carb float due to the tip-over.
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post #6 of 8 (permalink) Old 09-16-2016, 11:07 AM
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yup on the stuck float,also coulda stirred up some **** in the tank and is making the float needle stick,sounds like it's flooding out on the rear cylinder,try Wolfie's blowback method

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post #7 of 8 (permalink) Old 09-16-2016, 05:54 PM Thread Starter
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This is the second time I've had to get it towed, but only one of many times I've been left stranded. Just one problem after another. It's a real challenge to get these bikes satisfied. Looks like a deep carb and petcock cleaning is in order, then some electrical testing?

I swear if I wasted more money buying Caltric...
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post #8 of 8 (permalink) Old 09-16-2016, 07:22 PM
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I have tow insurance on my bikes. Costs about $7 a year. Seems worth it since bare minimum on a tow is $100 typically.

The electrical system is the weak point on these bikes. Hopefully whatever the problem is there it is simple or a byproduct of the cylinder not firing.

As far as the carbs go, that tends to be just about every carb'd engine ever in my experience. Some carbs are easier to access than the Vulcan's though.
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