Rund Fine until Highway Speeds - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 7 (permalink) Old 04-28-2009, 10:09 PM Thread Starter
 
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Rund Fine until Highway Speeds

I just had my carbs re-built by a local shop after the floats kept sticking open. She starts instantly, idles fine, and otherwise runs fine up to about 45 MPH. At highway speeds however, it sputters, jerks, hesitates and otherwise jerks my head back and forth. If i slow back into the 40 MPH range, it runs normally.

MPG dropped from ~50 MPG to ~40 MPG on a 500 mile cross country trip yesterday. It is more than painful to ride her on the highway. Any ideas??

Mearaman
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post #2 of 7 (permalink) Old 04-28-2009, 10:14 PM
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Originally Posted by mearaman View Post
I just had my carbs re-built by a local shop after the floats kept sticking open. She starts instantly, idles fine, and otherwise runs fine up to about 45 MPH. At highway speeds however, it sputters, jerks, hesitates and otherwise jerks my head back and forth. If i slow back into the 40 MPH range, it runs normally.

MPG dropped from ~50 MPG to ~40 MPG on a 500 mile cross country trip yesterday. It is more than painful to ride her on the highway. Any ideas??

Mearaman
Take it back, you have a fuel flow or float problem.


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post #3 of 7 (permalink) Old 04-28-2009, 10:24 PM
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Just a though, you might want to check that vent tube that goes to the right side air box off from the carbs. Make sure its not out in the open where you can get a serious back flush of air and that its not botteming out, starving for air. Sound like that might be it to me, at least try that before having to take it back, if that doesnt fix the issue, hell yeah take it back.


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post #4 of 7 (permalink) Old 04-28-2009, 10:29 PM
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Yeah, could be either one of the above. Since they adjusted your float it sounds like it's now adjusted too shallow. Enough fuel for lower rpms but running out when you throttle up. Or it could be the vent hose.

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post #5 of 7 (permalink) Old 04-29-2009, 09:20 AM Thread Starter
 
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Thanks for your input! I'm planning on taking it back, but wanted to be a bit smarter

While riding, I did play with the fuel valve. At 70 MPH, it would run a good 20 to 30 seconds before starving if I shut off the fuel. Doing so didn't help the problem though.
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post #6 of 7 (permalink) Old 09-26-2009, 04:23 PM
 
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My friends bike has the same problem, only after the dealer cleaned the carbs. The moment you go above 65 mph the engine starves for fuel and it seems like a braking effect where you are thrown back and then boom the fuel starts to flow again. It happens everytime you twist the throttle. Have taken it back to the dealer again. Unfortunately, the dealer doesnt drive the bike in the highway to test it. He just drives it in the parking lot and says that everything is fine.
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post #7 of 7 (permalink) Old 09-26-2009, 09:58 PM
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Originally Posted by krravi View Post
My friends bike has the same problem, only after the dealer cleaned the carbs. The moment you go above 65 mph the engine starves for fuel and it seems like a braking effect where you are thrown back and then boom the fuel starts to flow again. It happens everytime you twist the throttle. Have taken it back to the dealer again. Unfortunately, the dealer doesnt drive the bike in the highway to test it. He just drives it in the parking lot and says that everything is fine.
Could be the same thing. Check the vent tube. If it's bottomed out it will cut the air flow and can't get enough fuel delivery at higher rpms under load. Pull it out of the right air box and cut the end at a 45 degree angle so it can't bottom out. If that doesn't fix it, then maybe the floats are not adjusted right or the fuel tank vent might be clogged...

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