Here we go "AGAIN" - Page 4 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

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post #31 of 42 (permalink) Old 05-18-2020, 07:58 AM
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Pretty good time for an engine pull!

You could verify the valve is leaking with an air pressure test. Need compressed air and a fitting that will thread into a spark plug hole.

You put air pressure into a cylinder, rotate crank to where all valves are closed, TDC of compression stroke, then listen for air escaping intake or exhaust.

Once the head is removed, you can fill the areas behind each valve with liquid to see if it leaks into the combustion chamber over time. Liquid like gasoline, alcohol, or probably even water.

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__________________________________________________ ____________
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post #32 of 42 (permalink) Old 05-18-2020, 08:32 AM Thread Starter
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Originally Posted by Spockster View Post
Pretty good time for an engine pull!

You could verify the valve is leaking with an air pressure test. Need compressed air and a fitting that will thread into a spark plug hole.

You put air pressure into a cylinder, rotate crank to where all valves are closed, TDC of compression stroke, then listen for air escaping intake or exhaust.

Once the head is removed, you can fill the areas behind each valve with liquid to see if it leaks into the combustion chamber over time. Liquid like gasoline, alcohol, or probably even water.
yeh i seen some videos on valve leak test with fuel. The head was off the bike tho. Not sure if it could be done on the bike. Altho im sure if you could see the valve ports you might have some hope. Pretty neat idea with the air test. I might give that ago while i am waiting for my gauge to come
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post #33 of 42 (permalink) Old 05-18-2020, 09:52 AM
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Originally Posted by Spockster View Post
Pretty good time for an engine pull!

You could verify the valve is leaking with an air pressure test. Need compressed air and a fitting that will thread into a spark plug hole.

You put air pressure into a cylinder, rotate crank to where all valves are closed, TDC of compression stroke, then listen for air escaping intake or exhaust.

Once the head is removed, you can fill the areas behind each valve with liquid to see if it leaks into the combustion chamber over time. Liquid like gasoline, alcohol, or probably even water.
yeh i seen some videos on valve leak test with fuel. The head was off the bike tho. Not sure if it could be done on the bike. Altho im sure if you could see the valve ports you might have some hope. Pretty neat idea with the air test. I might give that ago while i am waiting for my gauge to come
Just make sure the threads are correct on your air fitting, don't want stripped plug holes.

A couple of times, I've made a fitting with an old spark plug, but it's a compromise. Can end up too leaky.

2003-21k mi
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__________________________________________________ ____________
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 #34 of 42 (permalink) Old 05-21-2020, 08:14 AM Thread Starter
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Problem found. This is definatly one for the record books. Ok so pulled the carbs again to take a look. Pulled the jets from both sides and low and behold the main jets are screwed. I obviously seriously over tightened them. In my defence.. ok i dont have any im an idiot lol. Judge for yourself by the pics. I await your roasting 😂
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post #35 of 42 (permalink) Old 05-21-2020, 08:49 AM
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Problem found. This is definatly one for the record books. Ok so pulled the carbs again to take a look. Pulled the jets from both sides and low and behold the main jets are screwed. I obviously seriously over tightened them. In my defence.. ok i dont have any im an idiot lol. Judge for yourself by the pics. I await your roasting 😂
While that's not good, I'm struggling to figure out how that would cause constant popping from one carb. A lean sneeze if fuel doesn't flow well, but only when the throttle is opened and just one pop.

Might check to see if the carb body is cracked near the jet holes.

Don't be too hard on yourself, this is one of ways we can learn.

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 42 (permalink) Old 05-21-2020, 09:24 AM Thread Starter
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Originally Posted by Will750 View Post
Problem found. This is definatly one for the record books. Ok so pulled the carbs again to take a look. Pulled the jets from both sides and low and behold the main jets are screwed. I obviously seriously over tightened them. In my defence.. ok i dont have any im an idiot lol. Judge for yourself by the pics. I await your roasting 😂
While that's not good, I'm struggling to figure out how that would cause constant popping from one carb. A lean sneeze if fuel doesn't flow well, but only when the throttle is opened and just one pop.

Might check to see if the carb body is cracked near the jet holes.

Don't be too hard on yourself, this is one of ways we can learn.
At the bottom of the tube it bottomed out against the fuel passage way. Fuel flow was definatly restricted. Im prusuming this is why it wouldnt rev passed 2k. Most of the little holes in the tubes are bent shut. My thinking is limited fuel causing no fire of the front cylinder. Eventualy the vapor from the limited fuel gets built up in the exhaust and eventualy igniting causing popping sound. Thats my thinking of it. I tried to take as clear as pic as possibal.
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post #37 of 42 (permalink) Old 05-21-2020, 09:38 AM
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Won't hurt to wait and see of new jets will cure it.

Can see they're deformed on the ends and around the emulsion holes, definitely not helpful to running.

2003-21k mi
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__________________________________________________ ____________
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Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #38 of 42 (permalink) Old 05-21-2020, 09:42 AM Thread Starter
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Won't hurt to wait and see of new jets will cure it.

Can see they're deformed on the ends and around the emulsion holes, definitely not helpful to running.
Just have to source them now pretty hard from ireland without having to wait weeks. Still waiting on a load of parts. So i will keep this updated as i go
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post #39 of 42 (permalink) Old 05-21-2020, 09:49 AM
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Yes the shipping is going to sting.

Arctic Cat and Harley have the same carb. Should be able to find jets below $10 each pretty easily, haven't looked for a while.

Stock jets? Maybe someone here has a pair?

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 #40 of 42 (permalink) Old 05-21-2020, 11:56 AM Thread Starter
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Yes the shipping is going to sting.

Arctic Cat and Harley have the same carb. Should be able to find jets below $10 each pretty easily, haven't looked for a while.

Stock jets? Maybe someone here has a pair?
yes stock jets and the carb rebuild kit i ordered dont have them in it. Typical. 62 euro from the netherlands for the 2 of them. 😲. I might check for harley ones. Might be easier to get. Is there a specific model i should search?
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