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A theory - or common sense

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4.3K views 13 replies 6 participants last post by  OleDirtyDoc  
B
#1 · (Edited)
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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M
#2 ·
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.
 
B
#4 ·
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
 
G
#6 ·
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.
 
B
#5 ·
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?
 
M
#8 ·
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.
 
#12 ·
the tw200 is a Yamaha dirt bike.the petcock bolts right on our bikes,but you need to plug the vacuum line

Sent from my LGL34C using Tapatalk
 
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#14 ·
Gotta get the motor over to my place, that is pretty much what I'm waiting on

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