No performance past 5k RPM - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 55 (permalink) Old 12-21-2013, 11:09 AM Thread Starter
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No performance past 5k RPM

Backstory

Bought this bike in June, knowing it needed a little love. Turns out it needed a lot more love than I expected. I've replaced: wiring harness, battery, R&R, front brakes, key ignition, junction box. Just when I thought I had everything running, bike broke down on trip to NY from DC. The way it was acting I assumed it was carb related (last thing I haven't touched). After pulling the carbs decided to also perform the ear shave procedure. After finding nothing wrong with the carbs I checked the gas in the tank and it turns out I had bad gas (water in the gas) from a mom & pop gas station that I stopped by on my trip.

Problem

The ear shave went off without a hitch. Airbox removed, K&N fliters installed, I cleaned the carbs while I had them off (and re-jetted per the instructions). Shimmed the needles, etc. Re-assembled everything. Bike starts great, tweaked the air/fuel mixture needles since I don't have stock exhaust and it was burning a little lean.

Now, when I get out on the road, in fifth gear, I can open the throttle all the way and get no response. It's hard to get the bike much past 65 MPH/5K RPM. This saddens me since I ride on the highway a lot. I'm not sure exactly what needs to be addressed or fixed. It appears the air/fuel screw is really only for the pilot jet, and this is a problem with the main jet. I can't tell if maybe it's getting too much air during high speeds and not enough gas?

I'm really not sure how to proceed and I can't reverse the procedure since the airbox was cut for removal.
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post #2 of 55 (permalink) Old 12-21-2013, 02:24 PM
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The vent line that went to the right ear needs to be tucked into a place that doesn't get air turbulence. Some people stick a filter on the end of it and then shield off the front side of the filter from the wind, or others (as myself) have just tucked the hose into the frame under the gas tank, while even others use the gas tank vent.
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post #3 of 55 (permalink) Old 12-21-2013, 03:58 PM Thread Starter
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Do you have a picture of this vent hose? There was the crankcase filter line that connected to the front of the forward cylinder that has a filter on it now, and the carb vent has a filter as well. I didn't see any other lines, but it's been about two weeks since removal. Where on the bike does the line go to?
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post #4 of 55 (permalink) Old 12-21-2013, 05:21 PM
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carb vent hose.. you nailed it.. is that hose out in the wind?
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post #5 of 55 (permalink) Old 12-21-2013, 06:52 PM Thread Starter
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It was attached to an Emgo Crankcase filter (amazon.com/Emgo-Crankcase-Vent-Filter-14-20900/dp/B0022ZZHG8) that was attached to the side of the frame where the right ear was. I pulled the tube off the filter and placed it under the tank with the opening facing the back of the bike, while the performance was slightly better still wasn't able to get the bike past 55mph/ 4.5KRPM with the throttle fully open.

Could the shims contribute to this at all? I may try removing/adding more to see if that has any affect.

Last edited by marcoceppi; 12-21-2013 at 06:54 PM. Reason: clarifications
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post #6 of 55 (permalink) Old 12-21-2013, 07:57 PM
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Quote:
Originally Posted by marcoceppi View Post
It was attached to an Emgo Crankcase filter (amazon.com/Emgo-Crankcase-Vent-Filter-14-20900/dp/B0022ZZHG8) that was attached to the side of the frame where the right ear was. I pulled the tube off the filter and placed it under the tank with the opening facing the back of the bike, while the performance was slightly better still wasn't able to get the bike past 55mph/ 4.5KRPM with the throttle fully open.

Could the shims contribute to this at all? I may try removing/adding more to see if that has any affect.
You still may not have the vent in 'dead' air.

Yes shims + too large of jets can delay the main/intermediate circuit long enough to bog out. I recently was asked to help with exactly that situation, however they had went way farther than the normal advise given here.

What is your combo, mods, etc.
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post #7 of 55 (permalink) Old 12-21-2013, 08:06 PM
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I re-read your OP. Does the pilot circuit work right? Mine will easily run freeway speeds (65-75) on the first 25% of throttle.
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post #8 of 55 (permalink) Old 12-21-2013, 08:21 PM
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post #9 of 55 (permalink) Old 12-21-2013, 10:02 PM
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Sounds like a vacume leak probably in the carb to head rubber boots.

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post #10 of 55 (permalink) Old 12-21-2013, 10:26 PM
..have a vulcan good day!
 
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Quote:
Originally Posted by FoolAmI View Post
Sounds like a vacume leak probably in the carb to head rubber boots.
.....from prior experience.... that can do it .


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