Need help diagnosing.... - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 21 (permalink) Old 05-03-2012, 04:00 PM Thread Starter
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Need help diagnosing....

Ok so i have a 86 vn750 and ive had it about a year. I rode it for a few months last year and other than a few cooling issues that were resolved, it has ran fine.

Around february this year i noticed gas leaking out of the airbox after sitting in storage all winter. I assumed this was due to a stuck float valve.

The past month i have gone through the bike cleaning, lubing etc....

I had the carbs out, cleaned thoroughly (jets, floats, etc)

I finally got the bike all put back together and it will start right up and idles fine, then start to get a little sputtery as if it is flooding out and it dies.

I noticed that there is gas coming from the air box again......WTF ( its a little oily)

Then i cant get it started back up unless it sits for a while

I checked the plugs (new mind you) and they look a tad on the dark side but not wet or black.

There is suficient vacuum to pull gas from the tank.

Petcock not leaking.

carbs are clean

new battery, spark plugs, fresh gas

and theres no gas out the exhaust

I seriously have no clue where to begin im getting so sick of this bike and if i have to pull the carbs again for a third time im going to set the bike on fire

Last edited by SScheuerman; 05-03-2012 at 04:04 PM.
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post #2 of 21 (permalink) Old 05-03-2012, 04:35 PM
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I know your pain, carbs are not fun on these bikes. Doing the ear shave made it a lot easier to get them in and out. When you say there is fuel leaking from the air box I'm assuming you mean the surge tank not the ears right? Also while shes idleing if you blip the throttle and release does it return to idle or drop below the idle rpms? I'm assuming you checked to make sure the choke is off and not sticking right? Also My recent nightmare was because the front float was not set correctly, it was way to high and allowing the bike to constantly run rich. To check this get a clear container or bottle. Hook a hose up to the carb drain and open the bleeder till it stops dripping fuel, mark a line empty container and do the other side, they should let out the same amount of fuel. If not then a float adjustment may be needed. Sorry for being so long winded.

86 Vn750
Coastered
De-Goated
Ears shaved
"Custom Pipes"
"Custom Seat"
Apes
Stator Mod
Malteese led Turn Signals (Rear)
Paid 750.00$ for her in 2005 w/ 9k
Currently @ 23k and counting

Last edited by Stones750; 05-03-2012 at 04:59 PM. Reason: more info
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post #3 of 21 (permalink) Old 05-03-2012, 05:01 PM Thread Starter
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Quote:
Originally Posted by Stones750 View Post
I know your pain, carbs are not fun on these bikes. Doing the ear shave made it a lot easier to get them in and out. When you say there is fuel leaking from the air box I'm assuming you mean the surge tank not the ears right? Also while shes idleing if you blip the throttle and release does it return to idle or drop below the idle rpms? I'm assuming you checked to make sure the choke is off and not sticking right?
The gas is coming out of the left side ear by means of the surge tank. Im sure it would be both ears however it is leaned to one side with the kickstand.

choke is working fine and disengaging properly.

As far as the rpms dropping after blipping the throttle goes, if i remember correctly it did have a slight sputter once i let off the throttle but its hard to tell due to the fact that the idle (throttle stop) hasnt been adjusted.

Right now it wont start so i cant tell.
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post #4 of 21 (permalink) Old 05-03-2012, 05:14 PM
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Sounds like the petcock not working right and the float stick allowing petrol to flood the bike
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post #5 of 21 (permalink) Old 05-03-2012, 05:17 PM
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Did you check the float level when the carbs were off?

I would quickly check that the choke plungers are clean and that the rubber isn't cracked before taking the carbs back off.

EDIT:

Were the rubber tips of the float needles in good shape?

I think what I'd do first is hook up a clear vinyl hose to the drain on the bottom of the carb, and string it up beside the carb with some wire. open the drain screw and let the hose fill up with gas from the carb, if the gas goes above the float chamber you'll know what your problem is.

You might need to pull the vacuum hose off the carb that goes to the petcock and suck on it with a syringe or your mouth.

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1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings

Last edited by Roach; 05-03-2012 at 05:26 PM.
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post #6 of 21 (permalink) Old 05-03-2012, 05:17 PM
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Well I'd try to see how much fuel comes out of each carb as it sits, also make sure the petcock isn't set to "prime". If more fuel comes out of one side than the other then its a float issue. You can also try to remove all the lines from the petcock with the adjuster set to on. No fuel should come from the petcock after the hoses are off. More than likely I'm thinking the floats sticking or needs to be adjusted per the manual.

86 Vn750
Coastered
De-Goated
Ears shaved
"Custom Pipes"
"Custom Seat"
Apes
Stator Mod
Malteese led Turn Signals (Rear)
Paid 750.00$ for her in 2005 w/ 9k
Currently @ 23k and counting
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post #7 of 21 (permalink) Old 05-03-2012, 05:42 PM Thread Starter
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ok ill give the "amount of fuel out of overflow" and "hose draining higher than the float level" a try,

The choke plungers are clean. the rubber looks new around them. Im sure the petcock is working as it should. fuel only flows when suction is applied to middle fitting.

i inspected the float valves when i cleaned them. The rubber looks perfect, the seats do not have any worn grooves, and there is an airtight seal when gently pressed into the seat.
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post #8 of 21 (permalink) Old 05-03-2012, 05:55 PM
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You still have a float that isn't seating right or out of adjustment. The petcock isn't responsible for flow control, that is all done by float action. The petcock has nothing but on or off as determined by vacuum. Unfortunately, I think your carbs need attention. I've been there and I know it sucks. Had those damn carbs out multiple times with a lot of bad words in between. Best of luck.

Dave

Mods:
Jetted, shaved & coastered
Home made under-tank single filter
Converted ACCT's to manual (thanks wib714)
Dual vac lines on petcock (my cure for ticking)
LED tail/plate lights
Relocated helmet lock to license plate

Added stuff:
Customized hard bags w/ lights
Chrome levers
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LED running lights
Home made 'Vita-Volt' meter
Foot rests on engine guard
Tunes

Hmm....she was on the back when we left.... ??
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post #9 of 21 (permalink) Old 05-03-2012, 06:16 PM Thread Starter
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ok i measured the fuel out of the carb drains. The fuel levels are almost identical.

Let me clarify, gas isnt leaking as if the a float is stuck open. Gas flowed out the airbox after idling for about 5 minutes.

The proiblem right now is the bike will not start at all. Battery volts are mint, starter is turning the bike over. It has fuel, spark, compression but wont run.

A few times trying to start it there was a puff of exhaust out of the airbox, and there were a few loud backfires but it will not idle.

im at my limit for frustration. I have always fixed my own cars, bikes, whatever myself without a problem, i am very mechanically inclined and the fact that this bike is stumping me completely is baffling
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post #10 of 21 (permalink) Old 05-03-2012, 06:41 PM
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Quote:
Originally Posted by SScheuerman View Post
It has fuel, spark, compression but wont run.
The only thing left is air.

The air filters are not clogged?

There's nothing obstructing airflow to the carbs?

Perhaps the floats are just filling the bowls too much?

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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