Bike not staying running?? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 17 (permalink) Old 12-15-2013, 09:52 PM Thread Starter
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Bike not staying running??

Okay the background; traded for this VN700 for my gal to ride, went through it replacing missing parts, fixing things, and customizing it for her. I did an ear shave, has aftermarket (de-goated) exhaust, so I did not re-jet the carbs, at her command.
I did go through and clean them, as well as replacing the inlet fittings, after reassembling, I backed out the mixture screws 2-1/2 turns.
After a few minutes of cranking the bike, I get it to start, however when I give it throttle, it dies. I could start and let it idle to warm up, then I could manipulate the throttle giving quick, small twists to get it past dying and then to rev on up, but if I revved and held it at a high rpm, the front cylinder would backfire, and it seemed like the front cylinder was not getting as hot as the rear ( judging by the exhaust) but it idled pretty smooth.
I looked at the carbs a little closer, and the choke was very stiff and kind of sticking. So I removed them and loosened the choke lever screws, which helped a little, but they still seem awfully stiff?? Is there supposed to be some type of return spring other than the little round ones on the shafts?
While I had the carbs off I went ahead and backed out the mixture screws another 1/2 turn to a total of 3. It seemed to start better and stay running with better throttle response.
But now, my new clear hoses that seemed to be tight enough not to be clamped, were leaking. The supplied spring clamps were just barely too small, I got FI clamps and clamped the lines on the petcock and at the carb inlets.
And added two small inline filters.
Now I have a very difficult time starting it and it dies as soon as it does. I guess I'll start by removing the filters. I'm in SE Alabama at 350' above sea level, any recommendations for a mixture setting, or should I be looking at something else (choke problem)?
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post #2 of 17 (permalink) Old 12-15-2013, 10:16 PM
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Quote:
Originally Posted by bamaboy View Post
Okay the background; traded for this VN700 for my gal to ride, went through it replacing missing parts, fixing things, and customizing it for her. I did an ear shave, has aftermarket (de-goated) exhaust, so I did not re-jet the carbs, at her command.
I did go through and clean them, as well as replacing the inlet fittings, after reassembling, I backed out the mixture screws 2-1/2 turns.
After a few minutes of cranking the bike, I get it to start, however when I give it throttle, it dies. I could start and let it idle to warm up, then I could manipulate the throttle giving quick, small twists to get it past dying and then to rev on up, but if I revved and held it at a high rpm, the front cylinder would backfire, and it seemed like the front cylinder was not getting as hot as the rear ( judging by the exhaust) but it idled pretty smooth.

I looked at the carbs a little closer, and the choke was very stiff and kind of sticking. So I removed them and loosened the choke lever screws, which helped a little, but they still seem awfully stiff?? Is there supposed to be some type of return spring other than the little round ones on the shafts?
While I had the carbs off I went ahead and backed out the mixture screws another 1/2 turn to a total of 3. It seemed to start better and stay running with better throttle response.
But now, my new clear hoses that seemed to be tight enough not to be clamped, were leaking. The supplied spring clamps were just barely too small, I got FI clamps and clamped the lines on the petcock and at the carb inlets.
And added two small inline filters.
Now I have a very difficult time starting it and it dies as soon as it does. I guess I'll start by removing the filters. I'm in SE Alabama at 350' above sea level, any recommendations for a mixture setting, or should I be looking at something else (choke problem)?
Front cylinder backfiring.... possibly not receiving constant spark ???
Stiff Choke.... Linkage or with cable attached ?
Have you checked fuel flow to carbs ? Search the threads on how to check flow rate...there was good discussion on the subject a few months ago.
...others who are better troubleshooters will probly chime in here soon.


'86 VN750 13,700 mi -Stock
-Purchased 2008 w/8800mi
Replaced ALL Cables . Kuryakyn LED Voltmeter
SilverStar Ultra 9003/HB2 H4 Headlamp, Jardine Fwd Controls,
Iridiums DPR7EIX-9 & Wires, Tuxedo Mod, Coil Mod, P/U Sensor Mod, Fork Seals,
Splines Lubed - 11/4/2012 - MF AGM Battery
Additional Flashing LED Brake Light on Trunk
Dampers went out @ 13+K !
After TOC MCCT's..... so amazingly quiet I discovered a rattling heat shield on my stock exhaust !
...have a vulcan good day!
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post #3 of 17 (permalink) Old 12-15-2013, 10:33 PM
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The first thing I would do is turn the petcock to prime. see if that changes it. I believe you can take the front gas hose off at the carb. See if you have gas flow.
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post #4 of 17 (permalink) Old 12-15-2013, 10:45 PM
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btw...fwiw....I utilzed “ Clear Fuel Line & 3/16 “ Clear Vacuum Line (off the roll) purchased from a large hardware store ie: Ace or True Value.
Clamps were not needed, but for assurance I put clamps on the carb connections anyway.


'86 VN750 13,700 mi -Stock
-Purchased 2008 w/8800mi
Replaced ALL Cables . Kuryakyn LED Voltmeter
SilverStar Ultra 9003/HB2 H4 Headlamp, Jardine Fwd Controls,
Iridiums DPR7EIX-9 & Wires, Tuxedo Mod, Coil Mod, P/U Sensor Mod, Fork Seals,
Splines Lubed - 11/4/2012 - MF AGM Battery
Additional Flashing LED Brake Light on Trunk
Dampers went out @ 13+K !
After TOC MCCT's..... so amazingly quiet I discovered a rattling heat shield on my stock exhaust !
...have a vulcan good day!

Last edited by WilliamTech; 12-15-2013 at 10:48 PM.
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post #5 of 17 (permalink) Old 12-15-2013, 10:49 PM
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Vacuum leak? ... also check petcock vacuum, if equipped.

The choke should have some friction, it should stay where you set it, but nudge easily for adjustments as it warms. Cables could be dried up.

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Last edited by Spockster; 12-15-2013 at 10:51 PM.
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post #6 of 17 (permalink) Old 12-16-2013, 03:37 AM Thread Starter
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maybe choke was okay then, In my ignorance I thought you should have to hold it choked, and it would return when I let off the lever. I did use the clear fuel line, so I can see fuel flowing, I had to warm it to fit over the fittings, sealed first time with no clamps, but when I disturbed them, they leaked. My rear carb vacuum nipple got a cap, as tight as it was, it could very well be cracked, and the front vacuum hose going to the petcock is very short and barely makes the span, sooo I'll double check all that tomorrow.
How do you set the petcock to prime, and what is that doing? would there be any benefit of running both vacuum line to a "T" and then up to the petcock?
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post #7 of 17 (permalink) Old 12-16-2013, 03:41 AM Thread Starter
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Oh, one other thing I wondered about, when doing the ear shave I made my own coasters out of 1/4" steel, because the screws were so long, I left the reed valves in place, I figured it wouldn't matter, as they were blocked off. Am I okay in that thinking, or do they need to come out?
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post #8 of 17 (permalink) Old 12-16-2013, 05:23 AM
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Your coasters should be fine. I did mine the same way.

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post #9 of 17 (permalink) Old 12-16-2013, 07:35 AM
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hmm ear shave, degoted, and aftermarket exhaust, and no rejet... before I go out on a limb here.. what brand of pipes did you use? Cobra and Vance and Hines both recommend rejetting when using their pipes in most cases. and it is highly recommended to rejet when you mess with both intake and exhaust. I think your backfiring is because you are running way to lean.
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post #10 of 17 (permalink) Old 12-16-2013, 09:48 AM
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I agree with Slim.i would rejet.read the ear shave section I'm the vulcan verses

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