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Engine surge/pulse

86 Views 6 Replies 4 Participants Last post by  Buddy
So this vn750 I've been working on has got me stumped. The carb has been cleaned and rebuilt, it runs and idles great, and if you gun it it'll rev fine, but when revving slowly or riding it gets to 4500rpm and then starts pulsing and won't go any higher. It had been sitting about 10 years and the more I run it the better it seems to get. Is it possible that it just needs ran and cleaned out. I currently have chemtool B12 in it and it seems to be getting better. I tried to check the vacuum on the carbs but the manometer just rapidly bounces and can't get a reading. I adjusted air/fuel mix a little and seemed to help a touch. Just not sure what to do next other than run it and see if it improves. Thoughts?
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Make sure the fuel lines don't run uphill or have any loops.

Are the slides operating properly? Diaphragms seated correctly?

It sounds like it's not getting enough fuel flow to the carbs.
Maybe you need to run it see if that helps
Make sure the bowl vent from the two carbs is open and sitting in dead air (tucked into the frame rail is where I put mine)
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Are those the vents that go to the T, and then to the right ear?
Are those the vents that go to the T, and then to the right ear?
When mine did the pulsing turns out I had to rebuild the carburetors. I noticed that you did have them rebuilt, but is there a possibility during the install you may have upset something? Have you checked to make sure that your air vent is clear the one that runs from the top of the gas cap to the back of the gas tank that should be able to be blown through the hose in the back and fill air come out of that cone in the middle of the gas cap
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