wont rev past 4500 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 06-14-2011, 11:05 PM Thread Starter
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wont rev past 4500

i just bought a 1990 750 that had been sitting for a year. it started right up and idled fine but it did not have much power untill 5500 rpm. when i looked into it i found that the vacum line to the right side valve was split and it also did not have the line from the split on the carbs to the right air cleaner. i replaced both lines but now it will not rev up past 4500 but runs well on low end. any help would be great!
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post #2 of 7 (permalink) Old 06-15-2011, 12:12 AM
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I would make sure the vent hose of the right ear (air cleaner) is not bottomed out. Vacum leaks or blockages cause a lot of issues.

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post #3 of 7 (permalink) Old 06-15-2011, 02:24 PM Thread Starter
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i have checked that as well and cut it at a 45. i even tried to remove the line again to see if it would go back to the way it was and it didnt change back.... doesnt make sense to me! it may be time to take it in to the dealer. is there anything i can do to bypass the vaccum lines to the carbs?
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post #4 of 7 (permalink) Old 06-15-2011, 02:34 PM
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Well I did an ear shave after having some carb issues which helped the bike a lot but left me kinda lost because i jetted to high then reset did ear shave and had to do a lot of tuning. It did eliminate some vac issues because I now have no goats belly or air box. IMHO dealers dont like these bikes the carbs can be a pain lol you'll save a lot of cash doing it by your self. But what exactly do you mean it wont rev past 4500 is it stubleing there or is it messing up while riding near that rpm range? I ask because I had a similar problem and it was my needles not being raised or shimmed enough.

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post #5 of 7 (permalink) Old 06-15-2011, 11:25 PM Thread Starter
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once i got up to 4500 it would just cut out and want to die if i held the throttle and come back to life when i let of the gas. i got off early today and was able to find a shop that had an opening so i took it in. so i guess i will see what they say. hope it isnt to bad!
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post #6 of 7 (permalink) Old 08-05-2011, 04:26 AM
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hi jgarrison,been reading your posts,i have a similar problem,wondered if you ever sorted it and what it was. thanks
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post #7 of 7 (permalink) Old 08-05-2011, 05:19 AM
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Originally Posted by maloney View Post
hi jgarrison,been reading your posts,i have a similar problem,wondered if you ever sorted it and what it was. thanks
Did either of you run a compression test ,I was just wondering,the order for trouble shooting is always..Compression ,Ignition and then fuel.If you are down on compression, good spark and fuel mixture,won't help any thing.

And use a compression tester ,just because it will blow your finger off the spark plug hole doesn't mean it is up to snuff/I can't remember offhand how many psi it should be but it is in the manual.Low compression means low vacuum as well and your carbs are CV carbs that require a healthy vacuum signal to pull the slide up inside the barrel of the carb.

My next step would be to check for vacuum leaks,just because you are getting fuel thru the petcock does not necessarily mean it is good.It is a prime place to look for a vacuum leak ,especially check the hose going to the petcock,It may have a small hole in it and it could be soft and collapsing in on itself and not allowing enough fuel flow for higher rpm running.

Last but not least is check your float settings they may be set to the point where it is simply running out of fuel at higher rpm's.

I skipped over the ignition part because from what I gather from both of you guys is the engine is running well at lower rpms.

Some food for thought and I hope it helps one or both of you with your problems




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Last edited by denny6006; 08-05-2011 at 05:23 AM.
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