Ran great last time, now won't idle - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 13 (permalink) Old 06-23-2014, 07:41 PM Thread Starter
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Ran great last time, now won't idle

After months of marveling at what a great running bike I have, all the while reading about problems others are having and thinking I'm glad I'm not dealing with that, now my bike has a problem. At idle, she's only getting fuel to the rear cylinder. Last time out, she ran perfectly. About five miles from home I had to go to reserve. No problem, came home and put her in the garage. Haven't ridden for about ten days, fired her up today to run some errands. I noticed she didn't start as quickly as usual but didn't think much of it. She shut down at the first stop and every stop thereafter. Topped off with fuel and came back home. Gave her time to cool down and started investigating. Stator voltage good, about 14.5 volts at 4k rpm. Strong spark on front cylinder at idle, but the front pipe is much cooler than the rear so I'm convinced its a fuel problem. Plan to try Wolfie's back blow procedure to see if it helps. Any suggestions are appreciated.
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post #2 of 13 (permalink) Old 06-23-2014, 08:02 PM
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Quote:
Originally Posted by rsavant View Post
After months of marveling at what a great running bike I have, all the while reading about problems others are having and thinking I'm glad I'm not dealing with that, now my bike has a problem. At idle, she's only getting fuel to the rear cylinder. Last time out, she ran perfectly. About five miles from home I had to go to reserve. No problem, came home and put her in the garage. Haven't ridden for about ten days, fired her up today to run some errands. I noticed she didn't start as quickly as usual but didn't think much of it. She shut down at the first stop and every stop thereafter. Topped off with fuel and came back home. Gave her time to cool down and started investigating. Stator voltage good, about 14.5 volts at 4k rpm. Strong spark on front cylinder at idle, but the front pipe is much cooler than the rear so I'm convinced its a fuel problem. Plan to try Wolfie's back blow procedure to see if it helps. Any suggestions are appreciated.
Good call !


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post #3 of 13 (permalink) Old 06-24-2014, 12:04 AM
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Sounds a lot like GloryRider's current problem but he's not firing on the rear cylinder. A compression test shows he's only got 30 psi on the rear cylinder but 129 psi on the front. He is currently pulling the rear head to check the valves. You can read about it on his thread " When is a 750 a 375? "

Steve, I really hope your problem is less severe than Matt's.

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post #4 of 13 (permalink) Old 06-24-2014, 12:30 AM
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I'll 3rd the back blowing..

quite possible when you switched to reserve there was some crap in the gas that got past the fuel valve "straws" and into your carb. I've had this happen to me once before: ran low on gas, hit reserve, and it started running like crap. filled up and it didn't resolve the issue. Did the back blow, and suddenly fine again.

......I'd rather wake up in the middle of nowhere then in any city on earth.

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post #5 of 13 (permalink) Old 06-24-2014, 06:51 AM Thread Starter
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Plan to try that today. I'm think something got into the carb because when I had to switch to reserve, the gauge was still showing about a quarter tank of fuel so when she started to die I didn't immediately switch to reserve, thinking something else was wrong. I hope that's all it is, not too excited about another carb pull.

I forgot to add, it runs fine on the road so it's something to do with the low speed circuit on the front carb.

Last edited by rsavant; 06-24-2014 at 08:07 AM.
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post #6 of 13 (permalink) Old 06-24-2014, 03:44 PM Thread Starter
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Unsuccessful on the back blow, the Allen plug wouldn't come out. Promptly rounded out when I tried. I removed the pilot jet screw and sprayed carb cleaner in and also sprayed carb cleaner into the fuel line while cranking the engine. While doing this, engine began to smooth out, idle speed increased, and the front pipe was hot. Maybe it was just leaning out because the tank was off. Let it sit a while to allow carb cleaner to work, confident the problem was resolved. Installed the tank, she started up, still didn't run right and now she won't start at all. Carbs off, don't see anything noteworthy. Everything looks clean. Removed pilot jet and blew air through it just in case. This is strange, has been running perfectly until I had to go to reserve the other day. Again, all suggestions are appreciated.
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post #7 of 13 (permalink) Old 06-24-2014, 04:48 PM
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When I was flow testing my petcock, I noticed fuel would only flow to the front line until I blocked it off. In other words, the rear cylinder will get no fuel until the front carb is full.

If you only flow enough fuel to support one cylinder, only one cylinder will have fuel, not both run with low fuel levels.

I would flow test the petcock. Just me.
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post #8 of 13 (permalink) Old 06-24-2014, 09:26 PM Thread Starter
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But since it ran ok at highway speeds shouldn't that eliminate petcock fuel flow issues? The only problem was it wouldn't idle. Now it won't even start. By the way, I had the fuel lines off but the petcock vacuum line was still connected. I cranked the engine over and there was fuel from the petcock.

I was planning on a spline lube, not a carb pull!

Thanks for the help.
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post #9 of 13 (permalink) Old 06-24-2014, 10:35 PM
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I bet the backblow wouldda worked....regardless, ya need to make those drains active for future use....try using a non metric set of allens....sometimes when one is stripped, you can tap it in....
Can ya get a pair of needlenose visegriips on it ?....my 700 has slotted screws....sometimes with the allens, ya can grab em with the vise grips....

or...buy a cheepo allen and JB weld it in there....once its out replace it....My backblow is only a "quick fix"....you can do it fully by removing the carbs and doing a full rebuild/cleaning.....



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post #10 of 13 (permalink) Old 06-24-2014, 11:38 PM
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Quote:
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sprayed carb cleaner into the fuel line while cranking the engine. While doing this, engine began to smooth out, idle speed increased, and the front pipe was hot.
This is why I suggested to check your petcock. If you have good flow, it is all you need.
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