Vapor Lock??? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 03-05-2010, 12:09 AM Thread Starter
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Vapor Lock???

Rode to work 6:30 AM today, on the highway going about, well, forget about that part... but seemed to run out of gas, or maybe my battery was going, or whatever, but I pulled onto the right shoulder and the bike just died.

All the lights worked and the starter turned, but no go. Only had 98 miles on the odometer so I thought I should have gas, but maybe not. (I keep my petcock in the reserve mode until I'm close to empty, just to avoid getting crud in the tank). Called my wife to bring me some gas and called work to let them know I'd be late.

Then I remembered, the dreaded VAPOR LOCK! Opened the gas cap and waited a bit. Wouldn't start right away, guess because the gas lines were dry. Then after about 3 minutes, POWER!!!

Question for the group: Does vapor lock occur more easily when it's cold outside? Could something be crystilizing in the gas cap vent hole or something? That might cause a lack of fuel to the carbs. My baby runs excellently all the time, except for this incident. Got to work fine, made it home fine.

WEIRD!!! But definitely NOT COOL. I have to rely on my transportation, and this can't be allowed to happen or I won't ride my baby to work.

Rubyrick

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post #2 of 12 (permalink) Old 03-05-2010, 02:10 AM
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It sounds like the phantom out of gas syndrome you are describing all right. But that is not the same thing as a vapor lock, as I understand it.

A typical vapor lock occurs in hot weather in an automobile when it is idling or shut off and the fuel in the line from the tank vaporizes as it enters the oven like temperature of the engine compartment, so that the fuel pump cannot pump it. This is more common with the older cars with carbs and a mechanical fuel pump mounted on the motor, where it has to draw or suck the fuel forward from the tank, and has relatively low pressure of 5 to 10 PSI.

A modern fuel injected car has an electrical fuel pump inside the fuel tank and may push 50-60 PSI, and is not subject to the same threat of vapor lock, due also to a pressure relief fuel return line to the tank from the engine. I am not sure if our Vulcans are susceptible to vapor lock as I understand that term.

Your question about something (ice?) crystallizing in the tank vent hole is interesting though. The Phantom out of Gas Syndrome seems to me, to be caused by a vacumn condition in the tank, so the vent is the likely culprit. It may be time to drill that gas cap vent out a few thousandths.
JM2 cents worth.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

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Last edited by OlHossCanada; 03-05-2010 at 01:14 PM.
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post #3 of 12 (permalink) Old 03-05-2010, 03:36 AM
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You are correct about "vapor lock". It has nothing to do with tank venting. It happens on carbureted cars, when the fuel vaporizes in the fuel line and the pump. A fuel pump cannot pump vapor, so no gas gets to the carb. True vapor lock is very rare, and happens only under extreme conditions. Pouring cold water on the fuel pump and lines would usually clear it right up. I don't see any way a motorcycle can have vapor lock, because they don't have fuel pumps.

As far as gas tank venting problems, about the only way that can happen is if you still have the CA evap emissions crap on the bike (surely nobody still has that crap), or the vent hose is kinked or plugged up. The tank should always be vented directly to the atmosphere, through one of the hoses connected to the rear of the tank (I forget which one).

I have had my gas gauge show empty after riding only 100 miles at an indicated 85-90 mph, but there is still a little gas left in the tank. I have gotten 150 miles out of a tank when taking it easy. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
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post #4 of 12 (permalink) Old 03-05-2010, 03:39 AM
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There was a spate of carb icing up in cold weather in the UK a while ago. It seemed to be mainly a Kawasaki problem. I used to get it on a ZX6 that I had at the time.

That's what it sounds like to me. The carb ices up internally stopping the flow. When you've been stopped for a few minutes, the ice melts due to the warmth from the engine & flow starts again.

Ride free, stay safe

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post #5 of 12 (permalink) Old 03-05-2010, 09:53 AM
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Ruby is in Hollywood, Florida, so it's definitely not icing up.

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post #6 of 12 (permalink) Old 03-05-2010, 01:03 PM
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Actually, carb icing can be a problem well above freezing. It is caused by the evaporation of the air/fuel mixture going through the carb venturi. This results in a rapid loss of temperature and pressure, and can cause "flashing", the same thing that happens at the metering device in an A/C unit. Kawasaki put carb heaters on the Vulcan 1500 Classic to prevent this issue. It is a common problem on light aircraft, which all have carb heaters. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #7 of 12 (permalink) Old 03-05-2010, 02:10 PM
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Why does the VN750 need both a gas cap vent and the vent tube at the rear of the tank?

Or more to the point, why have so many threads suggested enlarging the opening in the cap vent to prevent the Phantom out of Gas Syndrome, when the rear tank vent that is there already, should not allow a vacuum to exist?

A person should be able to determine if the rear tank vent is open or plugged by blowing on the end of the hose.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/showthread.php?t=9127
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post #8 of 12 (permalink) Old 03-05-2010, 06:13 PM
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If it is the out of gas syndrome, try this quick fix. I did it and no problem since. If your fuel lines still run from the petcock as you look at it, right side goes to the front cylender and the left goes to the rear cylender. Rerout them and make them shorter so they do not have to go up and over the top of the engine to the carbs. It gives the carbs a better gravity feed drop to them. Just my two cents, I think this gives the gas a better chance of giving a good flow of gas to the carbs.

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post #9 of 12 (permalink) Old 03-05-2010, 10:57 PM
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Quote:
Originally Posted by OlHossCanada View Post
Why does the VN750 need both a gas cap vent and the vent tube at the rear of the tank?

Or more to the point, why have so many threads suggested enlarging the opening in the cap vent to prevent the Phantom out of Gas Syndrome, when the rear tank vent that is there already, should not allow a vacuum to exist?

A person should be able to determine if the rear tank vent is open or plugged by blowing on the end of the hose.
You are correct, the hose is the vent, assuming you have no evap crap on the bike. If you do, it will cause all sorts of problems. Once you have removed it, and just connect a hose onto the tank, with the other end of it open to the atmosphere, you have a tank vent. On CA models, the cap has some kind of vapor return system in it, that makes noise after parking it after a ride. It no longer does that after you s***can the evap crap. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #10 of 12 (permalink) Old 04-20-2010, 08:39 AM
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My bike is doing the same thing and when I'm done riding I can hear it making that whistling sound as it sucking air. How do I know if I got a CA model and how do I s##t can it??

Lumpy

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