Shocking driving and high irregular idles - Page 4 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
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post #31 of 47 (permalink) Old 07-07-2019, 02:14 PM Thread Starter
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Quote:
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I raise it myself by throttling. Also can u explain what the butterfly etc is? Im not familiar with the terms.

Also in the video that was max throttle.
In that case, it may be a bad diaphragm. That's the round rubber part under the round cover on top of the carb.

The butterfly is the flap that rotates open when you twist the throttle. The butterflies on both carbs should begin to open at the same time. It's the plate with two screws seen in the center of the carb below.

I would look at the diaphragms first.



Carb Diaphragm Part #1 below

Are the diaphragms the same as on a cbr1000f? I'm fixing that one and if their the same I'll take em out there and place em in the vn750 carb
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post #32 of 47 (permalink) Old 07-07-2019, 03:18 PM Thread Starter
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Is there any kit for the vacuum valve?
I'll tear open my carb tomorrow or the day after to see if it's the valve. Just saw those things cost 100+ each and don't have the money for em
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post #33 of 47 (permalink) Old 07-07-2019, 04:47 PM
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Do them one at a time, the needles are different sizes front/rear.

Should be able to get to them on the engine.

When you take the top off, try to see if the rubber is seated correctly all around, and there's a tab that lines up.

Pull the diaphragm, slide, and needle out together.

Gently flex the rubber in front of bright light to check for holes/cracks.

There are pairs of diaphragms on ebay at $50us per pair, but they come without slides. Some people say they're impossible to transfer the slides to, but there are websites that show how to do it. Haven't done it on this carb myself.

Diaphragm How-To
Keihin CV carburetor diaphram installation page for JBM Industries
That site says the 67mm diaphragm fits the CVK36 carb on the VN750.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
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Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #34 of 47 (permalink) Old 07-07-2019, 04:52 PM Thread Starter
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I've found this set of diaphram, im almost sure they fit but just in case, can you have a look at them?
https://www.ebay.com/itm/Set-2Pcs-Ca...IAAOSw945Zd92K

Edit: ''Should be able to get to them on the engine.'' Do you mean i can take them out with the carbs still stuck on the engine? I checked to be sure but it looks like its almost impossible to without taking the carbs out.

Last edited by Panarock; 07-07-2019 at 04:56 PM.
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post #35 of 47 (permalink) Old 07-07-2019, 05:00 PM
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I've found this set of diaphram, im almost sure they fit but just in case, can you have a look at them?
https://www.ebay.com/itm/Set-2Pcs-Ca...IAAOSw945Zd92K

Edit: ''Should be able to get to them on the engine.'' Do you mean i can take them out with the carbs still stuck on the engine? I checked to be sure but it looks like its almost impossible to without taking the carbs out.
Those look correct, just without the slides.

Yes, I didn't type that correctly, I meant without taking the carbs off.

However ... If you're not earshaved, no, you can't. Airbox will be in the way.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #36 of 47 (permalink) Old 07-07-2019, 05:05 PM Thread Starter
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just to make sure. with the slides, do you mean the metal part attached to the diaphragms? as on the picture?
https://images-na.ssl-images-amazon....L._SL1200_.jpg
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post #37 of 47 (permalink) Old 07-07-2019, 05:17 PM
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just to make sure. with the slides, do you mean the metal part attached to the diaphragms? as on the picture?
https://images-na.ssl-images-amazon....L._SL1200_.jpg
That's the slide.

When you pull that out of the carb, there's also a long needle sticking through the slide. (don't mix the needles up)

There are Harley CVK40 slide/diap. at $20 each, but not sure if they fit.

Also, there's a lift test on the diaphragms. You lift the slide and let it drop. The slide should have resistance when dropping, and you should hear air wooshing from the diaph.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #38 of 47 (permalink) Old 07-07-2019, 05:19 PM Thread Starter
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I'll report back after work tomorrow. gotta use the bike once more before i can take the carbs out and have a look.
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post #39 of 47 (permalink) Old 07-08-2019, 01:57 PM Thread Starter
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Alright, I checked the diaphragms, and they look brand new.

Also the motorcycle is undrivable now, what is shown in the video is happening even when the bike is cold. And at all rpm ranges.

Any ideas?
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post #40 of 47 (permalink) Old 07-08-2019, 06:47 PM
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The diaphragms are indexed and seated correctly?

I'm running out of ideas. If it's not fuel, you could take a look at the spark and see what it's doing.

Take an old plug and check each wire. Start it up and see how well it sparks, and what color the spark is.

Edit: See what happens if you pull the choke while it's running.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf

Last edited by Spockster; 07-08-2019 at 11:17 PM.
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