How adjust the air/fuel mix screw??? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 02-19-2008, 11:13 PM Thread Starter
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Question How adjust the air/fuel mix screw???

I was moving the front carb air/fuel mix screw, now the front cylinder sound like no power and the bike is leaking a lot gas in the front exhaust pipe, the rear cylinder sound good, but I would like it make a really good adjustment and performance on the carbs, somebody can help me? also I install air cut diaphragm valves and o rings.

1989 Vulcan 750
Bobber style.
33000 miles,
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post #2 of 8 (permalink) Old 02-20-2008, 07:11 AM
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Sounds like something's sticking in your front carb - float valve or one of your new installments. For the air/fuel adjust screw, turning it clockwise will reduce the fuel:air ratio; turning it counterclockwise will increase the ratio (i.e., more fuel to air compared to when the screw is in further). You might try bottoming out the screw (turn it clockwise gently until it bottoms out; then back it out 1 5/8th turns - factory setting). But I'm guessing you might need to pull the carbs and see if the rebuild was ok. You shouldn't get that kind of flooding just from the air/fuel screw.

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post #3 of 8 (permalink) Old 02-20-2008, 10:34 PM
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Remember too that this adjustment only adjusts the idle mixture. Once you open the throttle, the internal jets take over and by pass the adjustment screws.

Jim W
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
21480 Miles
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post #4 of 8 (permalink) Old 02-20-2008, 10:58 PM
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Quote:
Originally Posted by Sky Rider View Post
Remember too that this adjustment only adjusts the idle mixture. Once you open the throttle, the internal jets take over and by pass the adjustment screws.
That is not entirely true. Idle circuit is still sending fuel to the engine..the percentage of how much this effects the engine goes down as the throttle opens of course.
This is true for all the circuits. As you open the throttle- The idle circuit is taken over by The Pilot jet , which slowly gets "overtaken" by the needle jet, then the main jet, but they all overlap some.

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post #5 of 8 (permalink) Old 02-21-2008, 08:34 PM
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True that, but adjusting the idle mixture won't affect the overall running of the bike. That's all I was trying to say. Too many people think that adjusting those mix screws will fix a rich or lean running bike in the overall sense which it won't. Does wonders for the idle and very low end though and helps reduce the popping on decel.

Jim W
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
21480 Miles
VROC #8542
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post #6 of 8 (permalink) Old 02-23-2008, 03:04 PM Thread Starter
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Today I was checking the carb,take off the front air duct and I looked the fuel flowing front the jet needle like a waterfall, How can I fix that?

1989 Vulcan 750
Bobber style.
33000 miles,
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post #7 of 8 (permalink) Old 02-23-2008, 10:51 PM
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Take off your carbs and clean and/or rebuild them. Something is not right inside and the only way to fix it is to take them apart and find the real problem and deal with it from there.

Jim W
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
21480 Miles
VROC #8542
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post #8 of 8 (permalink) Old 02-24-2008, 01:58 AM
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Cool

Quote:
Originally Posted by Sky Rider View Post
Remember too that this adjustment only adjusts the idle mixture. Once you open the throttle, the internal jets take over and by pass the adjustment screws.
if thats the case , why do we adjust it ?
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