Annoying minor surging and hesitation between 4,000 & 5,000 rpm - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 5 (permalink) Old 12-21-2007, 10:48 PM Thread Starter
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Question Annoying minor surging and hesitation between 4,000 & 5,000 rpm

My 1988 vulcan which I bought used 3 months ago runs kind of rough between 4,000 & 5,000 rpm. Outside of that range it's ok. I checked the air filters. The previous owner changed them before selling them to me and made the soaking them in oil mistake, so I spent some time wringing out excess oil. One of the rabbit ears was cracked and I sealed the crack. I backed the pilot screws out to 2.125. I threw a bottle of gumout into the tank & drove it 100 miles. Still the same poor behavior between 4,000 & 5,000 rpm.Any suggestions?
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post #2 of 5 (permalink) Old 12-22-2007, 12:53 AM
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What else has been done to the bike?Any exhaust mods or anything else been done to the bike?

Brian Manchester
'89 "GRIMM"

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post #3 of 5 (permalink) Old 12-22-2007, 03:13 AM
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There is a vent tube that goes into some slots in the right ear. Make sure ir is cut at a 45 degree angle at the tip and it is not 'bottomed out' against the inside of the ear. the surging and hesitation you talk ablout usually shows up if this vent hose isn't getting proper air flow. Also make sure the vent hose isn't kinked or pinched going into the ear.
Since you had the air filters off this is a very likely cause of the bike's performance once it gets into the higher rpms.

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post #4 of 5 (permalink) Old 01-11-2008, 10:34 PM Thread Starter
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I used genuine seafoam and mostly cured this problem.
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post #5 of 5 (permalink) Old 01-12-2008, 12:51 AM
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My guess is the vacuum/vent hose. My VN was a salvage bike that I put back together and it did the same thing until I followed the hose routing diagram.

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