A theory - or common sense - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
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post #1 of 14 (permalink) Old 03-28-2017, 06:00 PM Thread Starter
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A theory - or common sense

Hello all

I have a 98 vulcan 750 - I have a question regarding my carb - If anyone could shed some info on this I would appreciate it

The layout as follows - wanted carbs cleaned - no one wanted to touch the job - so I did it myself - all went fine for the removal, and the cleaning process within reason with a hic up or two but nothing monumental - not bad for first time i suppose.

the reinstall - different order - I have a second bike for parts - and I'm quite careful to study that bike before touching mine - I use it as a template just to ensure I'm in the correct form on anything I attempt.

As we took the carb out of the running bike I saw the throttle linkage area was sheared off - not a big deal as I had another carb on the parts bike - which i knew runs fine when purchased.

Now somewhere in the transfer of carb hoses I mucked up poorly - because once all went back together we started the bike and it ran for a few moments then fuel leaked every where including out the exhaust. Bike was off got it towed in lieu of trying again cause the lady upstairs from garage was non to pleased of the smell.

The mechanic is good a bike builder - but a harley bike builder - good man good hands but different bike all together.

I got the bike back he say it runs better than before bla bla bla......I rode the bike an instantly feel the difference in power. complete restriction on throttle accel. When i got the bike back to garage i study it further an notice he has added a T connect to my primary line from the petcock and from what I believe is the vacum line on the rear cylinder side of carb he linked the new T hose from vacum into the underside of gas tank.

I removed the hose from the gas tank area and feel a little less hesitation - but still no where what I once had. As I recall prior to disassembly that was a vacum line because it was capped off - and when I removed the cap the ran choppy - cap on bike smooth and full power...Now I have that vacum closed off and T into my primary. Bike runs as I said starts runs and rides - but not the same.

One note that I left out was when we started the bike on the initial reinstall of carb - fuel shot out that vacum section also - now its tight no leaks no error.

My question or theory is if i remove that added T section and cap off the vacum area would that be correct?...Or....did this mechanic find another way to hook up the carb - just with a bit of power loss - also what would be the turnout to machine over time - should I decide to leave it this way? I know my bike well I know it's not running to her full potential - until I have the chance to find a spot to do my tests I will not know. Perhaps you guys know better

Thanks I appreciate it
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Last edited by Brooklyn_Vulcan; 03-28-2017 at 08:10 PM. Reason: posting pics
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post #2 of 14 (permalink) Old 03-28-2017, 06:36 PM
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a 't' fitting on the inlet side of the bowls is not a disaster, but it means that the petcock has been replaced with a single outlet, or one outlet does not work.

there is supposed to be a 't' on the bowl vents (connecting them together), with the other end of the 't' going to a spot with dead air (right side air filter box if still using them, or under tank someplace if the airfilters/airbox have been removed).

there is a vacuum line from the left (front) carb to the petcock (stock petcock), and the same location on the right carb (rear) goes to emissions control crap (if its still installed), or plugged if thats stuff has been removed.

sounds almost like you had originally connected the fuel lines from petcock to the bowl vents. that will dump fuel all over the place.
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post #3 of 14 (permalink) Old 03-28-2017, 06:39 PM
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assuming its original petcock, one line to each carb, cheap petcocks with one output, I don't think they work, not enough gas to each carb using a "t"
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post #4 of 14 (permalink) Old 03-28-2017, 06:56 PM Thread Starter
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Originally Posted by michiganteddybear View Post
a 't' fitting on the inlet side of the bowls is not a disaster, but it means that the petcock has been replaced with a single outlet, or one outlet does not work.

there is supposed to be a 't' on the bowl vents (connecting them together), with the other end of the 't' going to a spot with dead air (right side air filter box if still using them, or under tank someplace if the airfilters/airbox have been removed).

there is a vacuum line from the left (front) carb to the petcock (stock petcock), and the same location on the right carb (rear) goes to emissions control crap (if its still installed), or plugged if thats stuff has been removed.

sounds almost like you had originally connected the fuel lines from petcock to the bowl vents. that will dump fuel all over the place.

Ok you just taught me thanks for that - what i call the primary line is infact a vacum off the petcock...which would strengthen my thought that the rear carb need be capped off as it once was....Im just concerned that fuel would shoot out the rear carb as it did before ..im not sure about us hooking up the lines to bowl vents cause it def seems the mechanic touched nothing further than what was needed to stop the leak...I knew how i left things and nothing seem to be touched other than added T...thanks so much
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post #5 of 14 (permalink) Old 03-28-2017, 07:01 PM Thread Starter
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so if understanding correctly - there are two vacum lines hooked together as one off the new T and thats what is restraining me?..because ?.almost like to positives working against ea other?....or too much draw of air in the line?
correct?
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post #6 of 14 (permalink) Old 03-28-2017, 07:15 PM
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Quote:
Originally Posted by jgs000 View Post
assuming its original petcock, one line to each carb, cheap petcocks with one output, I don't think they work, not enough gas to each carb using a "t"
Not really true. Myself and others run a replacement petcock with one output and T to each carb without issue (and have upped the pilot and jet sizes on top of that). If carbs drank gas at full gravity output from a fuel hose you'd be filling that tank in minutes.

OP- you could post pictures if you feel uncertain about any vac line plugged and your line routing.
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post #7 of 14 (permalink) Old 03-28-2017, 08:17 PM Thread Starter
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Originally Posted by michiganteddybear View Post
a 't' fitting on the inlet side of the bowls is not a disaster, but it means that the petcock has been replaced with a single outlet, or one outlet does not work.

there is supposed to be a 't' on the bowl vents (connecting them together), with the other end of the 't' going to a spot with dead air (right side air filter box if still using them, or under tank someplace if the airfilters/airbox have been removed).

there is a vacuum line from the left (front) carb to the petcock (stock petcock), and the same location on the right carb (rear) goes to emissions control crap (if its still installed), or plugged if thats stuff has been removed.

sounds almost like you had originally connected the fuel lines from petcock to the bowl vents. that will dump fuel all over the place.
Quote:
Originally Posted by gidaeon View Post
Not really true. Myself and others run a replacement petcock with one output and T to each carb without issue (and have upped the pilot and jet sizes on top of that). If carbs drank gas at full gravity output from a fuel hose you'd be filling that tank in minutes.

OP- you could post pictures if you feel uncertain about any vac line plugged and your line routing.
Thanks to my friend Jo - she posted the pics ...the first two are of the current running bike....the last is a carb i recently bought with the hoses on...you can see the rear carb side vacum line has nothing hooked to it...other than where a cap should go in my belief..I strongly think the carb purchased is correct...Im just at a loss cause I havent put in a bike yet...and yet the other set up runs..

wrong pic sorry of the purchased..thats the front carb side...my error

Last edited by Brooklyn_Vulcan; 03-28-2017 at 08:23 PM.
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post #8 of 14 (permalink) Old 03-29-2017, 08:37 AM
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ok, the pic of the carbs off the bike are correct as far as I can tell on the hoses. the nipple on left (front) carb will go to center of the petcock. the 2 that are 't'ed together are the bowl vents. they are correct, and the loose end of that hose goes to 'dead' air (under tank if your ear shaved, in right air filter box if not). right carb (rear) there is a vacuum line that is either capped off (if ear shaved), or goes to some emissions crap under seat if still stock.

on the 1st pic, I am going out on a limb and saying that they connected both vacuum ports (where petcock gets vacuum from on left carb) together. you only need the left carb connected to the petcock's vacuum nipple.

the underseat emissions crap is a vacuum operated valve that allows fresh air to be drawn into the reed valves (on side of head, large hose) to clean up emissions on decel conditions. also commonly causes lots of popping in exhaust.

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post #9 of 14 (permalink) Old 03-29-2017, 10:53 AM
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Do the tw200 petcock mod. Had ZERO problems with that.

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post #10 of 14 (permalink) Old 03-29-2017, 06:58 PM Thread Starter
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Quote:
Originally Posted by michiganteddybear View Post
ok, the pic of the carbs off the bike are correct as far as I can tell on the hoses. the nipple on left (front) carb will go to center of the petcock. the 2 that are 't'ed together are the bowl vents. they are correct, and the loose end of that hose goes to 'dead' air (under tank if your ear shaved, in right air filter box if not). right carb (rear) there is a vacuum line that is either capped off (if ear shaved), or goes to some emissions crap under seat if still stock.

on the 1st pic, I am going out on a limb and saying that they connected both vacuum ports (where petcock gets vacuum from on left carb) together. you only need the left carb connected to the petcock's vacuum nipple.

the underseat emissions crap is a vacuum operated valve that allows fresh air to be drawn into the reed valves (on side of head, large hose) to clean up emissions on decel conditions. also commonly causes lots of popping in exhaust.

very very interesting thanks...
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