carb problems??? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 21 (permalink) Old 05-23-2007, 07:52 AM Thread Starter
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carb problems???

I ride a 1986 vn750, which I have done a complete restoration,everything is stock except the exaust,used stock headers, built straight system,pipe on each side. I have been having a problem lately when running around 3000rpm,seems to have a flat spot,open the throttle a little and she runs great.
I have had the carbs.off and even taken them to the local dealer and service dept. was supposed to have gone through them and,says they are perfect. I know the carbs.need to be syncronized,but would this cause this problem? need any and all info.
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post #2 of 21 (permalink) Old 05-23-2007, 07:59 AM
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If the carbs/jets are clean, you can certainly rule out the carbs if you sync 'em and the problem goes away. Seems like you would notice other issues, though, such as your rpms jumping around a little at idle...anything like that happening?

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post #3 of 21 (permalink) Old 05-23-2007, 11:46 AM
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I don't recall if straight pipes without an ear shave effects jetting, but ya might read your plugs to see if you're running rich or lean....

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post #4 of 21 (permalink) Old 05-23-2007, 12:15 PM
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The pre-muffler with it's baffles would add back pressure, so I'm sure that straight through pipes even with mufflers and baffles have less backpressure, so there's going to be a change in the way the bike runs. My guess is it would be on the lean side since more air is going through. The rpms don't matter as much as how much throttle you're giving her when she hits a flat spot. If it clears up with more throttle, you've probably moved into the main jets. Someone more intelligent about these carbs can probably explain this better. If you give it a little choke when this happens and it smooths out, I'd say it's jetting problems.

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post #5 of 21 (permalink) Old 05-23-2007, 01:41 PM Thread Starter
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thanks for all your suggestions and ideas,I have not tried the choke thing,but I will. contacted the mechanic at the dealer,and he is suggesting that I have an exaust leak,I have been through this exaust thing before with him, my pipes are welded where they were connected to the stock headers,and have no leaks, bike ran good with straight pipesuntil about two weeks ago,I am out of ideas,might have to re-jet
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post #6 of 21 (permalink) Old 05-23-2007, 02:34 PM
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Could there be a possibility of a leak where the headers bolt to the engine?
And, like Curtis mentioned, have ya checked what the plugs look like?
What about the airfilters? They clean?


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post #7 of 21 (permalink) Old 05-23-2007, 08:00 PM Thread Starter
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I have removed the headers and checked the exaust manifolds for leaks and found none,re-installed the headers and pipes making sure there was no leaks,although the rear cylinder has started popping on decileration, which would indicate a possible leak. puzzled,puzzled
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post #8 of 21 (permalink) Old 05-23-2007, 08:43 PM
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Quote:
Originally Posted by Tater bug View Post
I have removed the headers and checked the exaust manifolds for leaks and found none,re-installed the headers and pipes making sure there was no leaks,although the rear cylinder has started popping on decileration, which would indicate a possible leak. puzzled,puzzled
Or you're possibly running leaner on the rear cyl. IF you need a talk-through for the carb sync, lots of folks here can get you through the process for pennies. Well, a dollar or two.

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post #9 of 21 (permalink) Old 05-26-2007, 08:11 AM Thread Starter
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well I worked on my bike all day yesterday, but to avail. I tried to sync. the carbs.but they would while at idle, but when rev.it to around 3200 thet would start to change,when back to idle the sync wouls be off again.tried to find an air leak,none found. done compression check front cyl 125 rear 142,only 22000 miles on clock.about ready to donate bike to goodwill.
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post #10 of 21 (permalink) Old 05-27-2007, 12:36 PM
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Have you checked to see if the carb boots to the heads are on right??

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