Idle Problem Back - With a Twist - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 14 (permalink) Old 04-17-2007, 07:48 AM Thread Starter
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Idle Problem Back - With a Twist

I thought I had an idle problem solved. Bike starts and runs fine. After riding for a period of time - bike is good and warm - idle drops when I come to a stop and eventually dies. Engine will restart if throttle is held open. Gumout and Seafoam seemed to solve problem (I thought), but it came back last night.

The twist is this: I thought I would leave the bike run and shut-off the fuel and empty the carbs. When I turned the fuel off, after a second or two, the idle came back up. Fuel on - a second or two passes - idle drops and starts to die. Fuel off - a second or two passes - idle picks up and seems to run fine.

What is going on?
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post #2 of 14 (permalink) Old 04-17-2007, 08:05 AM
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Sounds rich. What do the spark plugs look like ?

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post #3 of 14 (permalink) Old 04-17-2007, 08:26 AM
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sounds like you have some crud stuck in the float jet, flooding out at idle.
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post #4 of 14 (permalink) Old 04-17-2007, 09:37 AM
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I've seen other threads where it is suggested you run a high ratio of seafoam into the carbs, ie run for 5 to 10 min then shut it down and let the seafoam sit in the carbs overnight. Let it do it's work. Then run per normal one or 2 tanks with seafoam and this seems to clean the carbs/fuel system out well.

Most folks here will suggest you try this before anything more serious like tearing apart your carbs.

What year bike is it and is it the original fuel petcock?

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post #5 of 14 (permalink) Old 04-17-2007, 10:02 AM
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It sounds like the problem I had with the vacuum hoses that run between the floats on the carb.

I had a rip in one of the hoses and it caused the exact problem that you are describing.

The bad thing is that the only way to get at the hoses os to pull the carbs. Unless you have removed the surge tank.

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post #6 of 14 (permalink) Old 04-17-2007, 01:51 PM Thread Starter
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Just for info: the bike is a '92 with 8,500 miles on it. I bought it last year. I doubt the carbs have ever been off the bike.

I'm tending toward the flooding float bowl(s) idea. I just hate the idea of taking the carbs off and apart. I take that back, getting them back together and back on the bike is what bothers me.

Can pressure build up in the tank and force too much fuel into the float bowls? Jamie mentioned the vent tubes from the float bowls - if they are blocked or plugged, can that cause flooding? What are the chances of a damaged float or float valve?
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post #7 of 14 (permalink) Old 04-17-2007, 03:35 PM
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My problem was too much air. Only one hose had a hole in it causing an imbalance between the floats. I am pretty sure it was because they had cracked from age since my bike is an 88.

These are the ones that go into a T-connetor that goes into a hose that goes into a spot on the right air filter.

You might want to check the hose where it connects to the air filter.

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post #8 of 14 (permalink) Old 04-17-2007, 04:16 PM
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It is a good idea to check all your vacuum lines and fuel hose, vent hoses, etc. But don't ignore the seafoam suggestion above. That should be the first thing you do no matter what. Plus, you bike needs it anyway on a monthly basis, so you might as well start now. It could solve your problem.

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post #9 of 14 (permalink) Old 04-17-2007, 09:27 PM
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Sounds like your engine is running rich which fouls the plugs causing the engine to die. When you shut off the fuel, it leans out causing the idle to increase and then die once the fuel runs out.
I had similar problems and even with the Seafoam treatment, ended up taking the carbs off and cleaning them out. I never really found anything but the bike has run great since. That being said, try the Seafoam soak treatment anyway as it may still clear your problem. Many here have used it with great success. My experience seems to be the exception. It is much harder to get the carbs out than back in unless the boots are put back in wrong.
While the Seafoam is soaking, go ahead and inspect all the hoses going into the carb. Mine is a 93 and at the time it only had about 10K miles or so. I had replaced most of the hoses anyway as they had hardened and I didn't trust them.
Another thing you may want to check is whether or not you have the older Pri On Res petcock or the newer Off On Res petcock. I'm not sure what year they put the newer petcocks on but if you are running in Pri(me) with the older version, it could also contribute to rich running.

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post #10 of 14 (permalink) Old 04-18-2007, 10:31 AM Thread Starter
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First, I want to thank everyone who has offered suggestions. I really appreciate the fact that you have taken time to try to help me with this problem.

Here's an update: I decided to do some more "research" last night and took the bike out. It started and ran fine. I rode around for awhile and got the engine good and warmed up. I had to come to a stop at an intersection and I could feel the idle start to drop. This was confirmed when I saw the needle on the tach slowly drift downward. "Ah-ha!, I thought, it's somehow related to the engine temperature!" I opened the throttle to keep the engine at 2,000 rpm and got through the intersection. I thought I would head for home and see what I could do.

I had several more intersections where I had to stop. No problems. I got the bike home and left it running in the driveway waiting for the idle to drop and then die. It kept running.

I parked the bike and let it cool off for about an hour and a half. I took it out again and rode for another hour covering 50 miles. Great ride - and no problems. Got it home, let it sit, idled fine, didn't die.

I am beginning to think that my bike may have Alzheimer's and may just forget how to idle on occasion. Beats me....
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