Strange Carb Issue - Kawasaki Vulcan Forum : Vulcan Forums
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post #1 of 21 (permalink) Old 09-03-2017, 11:08 PM Thread Starter
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Question Strange Carb Issue

Hello All,

New to the forum, and hoping someone can suggest something that may be an issue on my bike.

96 Vulcan 800
7700mi

Exhaust is debaffled, and I did the "Scooterize mod" Attached is a picture of the result.

Factory needle, using a 52 pilot and a 170 main jet. I have adjusted the air/fuel screw as few as 1 turn and as many as 4 or 5, this issue doesn't seem to go away.

I have gone through the carb again and again, but I have one issue at this point that is blowing my mind. In different gears and at different times, I roll onto the throttle and when I am at roughly 25%, the bike starts breaking up. popping/spitting/sputtering and if I hold the throttle at that point, it just continues to do so and never clears up. It also wont really accelerate anymore until I go to probably 75% throttle, at which point it clears right up and pulls like a bat out of hell.

Additionally, when I am on the highway it seems to be even worse in 5th gear, which is problematic because I find that 25% is sort of a sweet spot for 70-75mph.

Thanks in advance.
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96 Vulcan 800
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post #2 of 21 (permalink) Old 09-04-2017, 03:05 AM
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There are two ideas:
1) Vacuum leak or a fuel petcock issue.
2) Too small fuel level in a float chamber which could be the result of first idea.
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post #3 of 21 (permalink) Old 09-04-2017, 10:49 AM Thread Starter
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Last night before making this post I took the carb off and checked the float level, as it was the one thing that I had not yet checked.

It was set around 17-18mm so I adjusted it down closer to 16.5.

Also I would think that if it was starving for fuel that I wouldn't be able to go full throttle and have it clear right up.

I will investigate the fuel petcock problem.

Thanks

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post #4 of 21 (permalink) Old 09-04-2017, 12:12 PM Thread Starter
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Just an update:

As a trial to see if the petcock was the issue, I pulled the vacuum line off the petcock and plugged it, and went on a short ride with the petcock in the prime position.

My thought is that if the petcock not flowing correctly was the issue, being the prime position should just supply fuel nonstop independent of any vacuum.

Results were basically the same, rides decent around town, but when you get on the highway the issue becomes more pronounced and it just runs horribly.

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post #5 of 21 (permalink) Old 09-04-2017, 01:07 PM
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If you have pulled them, what is the condition of the spark plugs?

"Don't force it. Get a bigger hammer."
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post #6 of 21 (permalink) Old 09-04-2017, 01:31 PM Thread Starter
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I may go ahead and replace them. I installed new ones about 1400 miles ago when I first got the bike, perhaps with all the changes I've made to the intake/exhaust I should have replaced them already.

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post #7 of 21 (permalink) Old 09-04-2017, 01:44 PM
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You may have some spark scatter due to vibration.
Try jumpering the two wires at the sidestand switch together and try again.
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post #8 of 21 (permalink) Old 09-04-2017, 01:55 PM
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Quote:
Originally Posted by DespicableDan View Post
I may go ahead and replace them. I installed new ones about 1400 miles ago when I first got the bike, perhaps with all the changes I've made to the intake/exhaust I should have replaced them already.
You may be right, but I was asking about the color and condition of the plugs as a clue to whether this is, in fact, a carburetor issue.

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post #9 of 21 (permalink) Old 09-04-2017, 03:56 PM Thread Starter
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Thanks for the tips.

I will check out those two items.

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post #10 of 21 (permalink) Old 09-05-2017, 02:03 AM
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Quote:
Originally Posted by DespicableDan View Post
Just an update:

As a trial to see if the petcock was the issue, I pulled the vacuum line off the petcock and plugged it, and went on a short ride with the petcock in the prime position.
* * *
Results were basically the same, rides decent around town, but when you get on the highway the issue becomes more pronounced and it just runs horribly.
I had similar problems on highway when I had a vacuum leak at manifold. The rubber holder which connects the carb to the manifold was not sealed. (The rubber gets old and hard. I ordered new one.). The engine got warm and started to suck outside air. I got lean and loss of power and extra heat in pipes. Try to check any vacuum leak on hot engine. Take some carb cleaner or starting fluid and carefully spray over Your manifold when the engine is idling. If rpms are changing, everything is trivial.
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