Stumbling, Flooding, Stalling - Enrichers / Air Cut off Valve / Diaphragms - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 13 (permalink) Old 08-15-2009, 10:45 AM Thread Starter
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Stumbling, Flooding, Stalling - Enrichers / Air Cut off Valve / Diaphragms

Hello All,

Sorry I haven't been doing a lot with the "social" side of the site - the fire, the accidents (yikes!) and so on. I've been swamped at work lately.

So - I started work again on the project bike. I did the ear shave, the degoat, the rejet/carb clean, etc. The bike kept flooding, then stumbling and dying when I tried to ride her.

Turns out, in addition to replacing the float needles, what I really needed to do was replace the diaphragms on the side of the carbs. They had significant cracks and holes in them.

Changing them out was easy - don't even have to take the carbs off the bike. Just unscrew the cap, pop the new valve, tiny O-ring, and spring in, and screw the cap back on. This also makes them easy to check.

The replacement parts can be found on ebay if you search for "diaphragm" or "air cut off valve". I'm not sure what they do exactly, but apparently having holes in them means flooding and stalling and uneven idle.

Now she fires right up and will maintain a steady idle.

Time to change out the coolant and the gas corrupted oil. Then maybe a ride today - hot damn.

Scheherazade
'86 VN750
MF Battery, Iridium Plugs, RR relocated, Voltmeter, 170/80/15 Kenda Kruz rear tire, DIY Samsonite hard bags, DIY shaved seat with Beaded seat pad ('cause that's how I roll) and the dreaded STATOR CHANGE.

Shining Black Bess '86 VN750, retired for parts after a fried stator and being knocked (kee-runch) in her parking spot.
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post #2 of 13 (permalink) Old 08-15-2009, 11:10 AM
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Nice - glad you figured it out - now I know what to look at if I ever run across the problem.
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Last edited by MisterPister; 05-11-2011 at 06:29 PM.
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post #3 of 13 (permalink) Old 08-15-2009, 12:52 PM
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Quote:
Originally Posted by skalding View Post

Time to change out the coolant and the gas corrupted oil. Then maybe a ride today - hot damn.
What was ut that gas-corrupted your oil? I'm sure you fixed the cause before you changed out the oil.

Rubyrick

MY BABY...
'05 VN750
16,000 miles +
Kawi tank bib
Kawi rear rack
Small windshield
DEKA M/F battery
VN750.com Grill Cover
LED license plate frame
Clear Alternatives LED brake light
Cortech mini tank bag on rear rack
Pirelli MT66 Tires: 110 front / 150 rear
Splines lubed when tires installed at 10,650 miles
Splines lubed again at 14,400 with stubby valve stem install

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Last edited by rubyrick; 08-15-2009 at 12:55 PM.
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post #4 of 13 (permalink) Old 08-16-2009, 03:36 AM
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Rick, the flooding carbs would cause gas in the oil
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post #5 of 13 (permalink) Old 08-16-2009, 04:48 AM Thread Starter
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Slim has it.

Unfortunately, it started flooding again after a Great test ride. I suspect the float needles have some kind of trash on them.

Can someone explain the physics of this? - shouldn't the petcock just shut off without vacuum? Meaning, how can I have a steady flow of gas out of the tank through the petcock, and into the carb?

I mean, that's what's happening, but I thought there couldn't be flow through the petcock without vacuum.

Scheherazade
'86 VN750
MF Battery, Iridium Plugs, RR relocated, Voltmeter, 170/80/15 Kenda Kruz rear tire, DIY Samsonite hard bags, DIY shaved seat with Beaded seat pad ('cause that's how I roll) and the dreaded STATOR CHANGE.

Shining Black Bess '86 VN750, retired for parts after a fried stator and being knocked (kee-runch) in her parking spot.
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post #6 of 13 (permalink) Old 08-16-2009, 05:03 AM
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Quote:
Originally Posted by skalding View Post
Slim has it.

Unfortunately, it started flooding again after a Great test ride. I suspect the float needles have some kind of trash on them.

Can someone explain the physics of this? - shouldn't the petcock just shut off without vacuum? Meaning, how can I have a steady flow of gas out of the tank through the petcock, and into the carb?

I mean, that's what's happening, but I thought there couldn't be flow through the petcock without vacuum.
Petcock will shut off, but the carbs will drain. Unless you have a pre 89' and petcock is set to "PRI:


85 VN700 "Old Yella"

REBUILT ENGINE
CUSTOM PAINT
VANCE & HINES CRUZERS
EAR SHAVED AND RE-JETTED W/K&N'S
DUNLOP ELITE K591 FRONT & REAR
VOLTMETER
SYNTHETIC BRAKE FLUID
SYNTHETIC OIL & GEAR LUBE
PLEXISTAR 2 WINDSHIELD
SPLINES LUBED
ACCT'S GREASED W/TOC SPRINGS
COASTERD
LEATHER SADDLE BAGS
LEATHER TOOL AND ROLL BAG
PICKUP COILS GAPPED AT .018"
NGK CAP, WIRES, IRIDUMS
BARNETT FRICTION PLATES & SPRINGS
CUSTOM GRIPS, MIRRORS, LEVERS
ORIGINAL STATOR & R/R 14.5v
DEKA MF AGM ETX15L

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post #7 of 13 (permalink) Old 08-16-2009, 06:29 AM
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hey lance...that isn't entirely true... mines a 92 with on, off and res.
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post #8 of 13 (permalink) Old 08-16-2009, 08:56 AM
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I thought gas flow was gravity feed and the vacuum helped suck out the gas faster than gravity alone during times of higher demand. If that is true then any leak post petcock will allow gas to flow by gravity through the petcock, unless the petcock is turned to OFF. Am I wrong, as my wife likes to tell me constantly?

Rubyrick

MY BABY...
'05 VN750
16,000 miles +
Kawi tank bib
Kawi rear rack
Small windshield
DEKA M/F battery
VN750.com Grill Cover
LED license plate frame
Clear Alternatives LED brake light
Cortech mini tank bag on rear rack
Pirelli MT66 Tires: 110 front / 150 rear
Splines lubed when tires installed at 10,650 miles
Splines lubed again at 14,400 with stubby valve stem install

Place your mouse on the X below and drag to the O

X
Even though you can't see Him, GOD is there! O
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post #9 of 13 (permalink) Old 08-16-2009, 11:54 AM Thread Starter
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Well, not to muddy the waters, but I have an 86 petcock (as far as I can tell - the bike's an 86, and I don't know if any of the POs did anything with the tank.).

I replaced the petcock diaphragm because of flooding earlier. Now I wonder if the petcock diaphragm is the wrong one or something. It fits, but is the petcock diaphragm the same for an 86 and a (for example) 92?

When I shut the bike off, I had gas leaking out of the right emigo filter (the new bike is shaved). It was like the tank was draining straight out into the carb with nothing stopping it. I am certain that the petcock was on the regular setting, not PRI. I toggled it between Res and regular just to see if anything would happen. Nothing did.

So I opened the drain on the bottom of the right carb, put a piece of vinyl tubing on it, and let it drain into a gas can. What a mess by that point though!

Anyone have any thoughts on why my tank is just draining through the right carb?

Scheherazade
'86 VN750
MF Battery, Iridium Plugs, RR relocated, Voltmeter, 170/80/15 Kenda Kruz rear tire, DIY Samsonite hard bags, DIY shaved seat with Beaded seat pad ('cause that's how I roll) and the dreaded STATOR CHANGE.

Shining Black Bess '86 VN750, retired for parts after a fried stator and being knocked (kee-runch) in her parking spot.

Last edited by skalding; 08-16-2009 at 11:56 AM. Reason: forgetfulness
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post #10 of 13 (permalink) Old 08-18-2009, 01:55 AM
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Quote:
Originally Posted by slimvulcanrider View Post
hey lance...that isn't entirely true... mines a 92 with on, off and res.
Sorry dude but it is entirely true!!! By your own admission your petcock does not have the "PRI" setting that was pre 89'. Pre 89's had a "PRI" setting instead of "OFF" which means "prime" it was a function to prime the carbs before you statted the engine. It bypassed the vacuum diapram and would let fuel flow.

They have the same diaphram and 0-rings but the selector is different. Just went through this last week with Hyper.


https://www.vn750.com/forum/showthrea...269#post111269






85 VN700 "Old Yella"

REBUILT ENGINE
CUSTOM PAINT
VANCE & HINES CRUZERS
EAR SHAVED AND RE-JETTED W/K&N'S
DUNLOP ELITE K591 FRONT & REAR
VOLTMETER
SYNTHETIC BRAKE FLUID
SYNTHETIC OIL & GEAR LUBE
PLEXISTAR 2 WINDSHIELD
SPLINES LUBED
ACCT'S GREASED W/TOC SPRINGS
COASTERD
LEATHER SADDLE BAGS
LEATHER TOOL AND ROLL BAG
PICKUP COILS GAPPED AT .018"
NGK CAP, WIRES, IRIDUMS
BARNETT FRICTION PLATES & SPRINGS
CUSTOM GRIPS, MIRRORS, LEVERS
ORIGINAL STATOR & R/R 14.5v
DEKA MF AGM ETX15L

Best Auto/Moto Insurance | Motorcycle Protection Today | FREE Trade-In Quote
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