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[oletrucks] "Vapor Lock" Summary

To: oletrucks@autox.team.net
Subject: [oletrucks] "Vapor Lock" Summary
From: The Perfesser <perfessr@songs.com>
Date: Sat, 26 Feb 2000 13:23:24 -0600
A week or so ago I wrote into this list to describe the problem I've had 
with my 49 Chevy half-ton conking out, and refusing to restart until after 
I'd towed it home.   I just want to write back now and thank everybody for 
their myriad suggestions, which ran the gamut from clipping clothes pins to 
the fuel line (to dissipate the heat) to cleaning out the gas tank of any 
accumulation of gunk to some electrical possibilities.

It was very gratifying to discover this list and get so many encouraging 
responses.  Thanks, everybody.

I'm not sure how many of the responses made it to the list itself (most 
seemed to be addressed to me personally) so here is a "digest" of the 
responses I got, and a few additional comments based on my own 
experience.  Perhaps other readers will find it useful.



>From: "David Krucas" <kruc@worldnet.att.net>
>
>It does sound like vapor lock. Vapor lock is caused by your gasoline
>changing from a liquid to a gas inside the fuel line before it gets to the
>carburetor. Gas goes from tank to fuel pump, then up over the engine to the
>carb. That's where it gets too warm. The cure is to reroute the line so it
>picks up as little heat from the engine and radiator as possible.
>
>Other things can cause your symptoms, too.  I had a problem when I ran my
>first '57 out of gas, and it picked up all the junk from the bottom of the
>tank. Carb shop rebuilt it and put a fuel filter in the line between the
>tank and the fuel pump
>- - - - - - -
>
>From: Passnb4U@aol.com
>
>   Since you mentioned your site bowl being empty, I'd pull the tank pickup
>tube and check the screen on it, also blow through the thube and make sure
>nothing is obstructed.



I got a few messages suggesting something in the gas tank gumming up the 
works before fuel made it to the pump.  But then, I recall that the little 
bubble on top of the fuel pump (which is a brand new version of the 
original) was full of fuel.  So, I don't think THAT's the problem, but I 
think I'll have the whole fuel system checked from tank to carburetor.


>One last thing, you're using a vented gas cap, aren't you?

Ummm...well, no, now that you mention it, I'm NOT using a vented gas 
cap.  I can see how a vacuum in the fuel line would cause the thing to 
stall and not restart, but the FIRST time I had this problem, I thought I 
was out of gas and opened the tank and poured a gallon in;  Didn't help at 
the time,although the mechanic who got the truck next morning started it 
right up.   So, even though the possible vacuum in the tank had been 
relieved, the problem persisted.  Or am I missing something re: the benefit 
of a  vented gas cap?



>- - - - - - - -
>
>From: JMungon@aol.com
>
>the trouble is usually in the engine bay where the fuel line passes near 
>the exhaust manifold or any other source of heat like the radiator or 
>hoses.....i have fixed this by positioning the  fuel line away from the 
>heat source....cut a piece of rubber fuel line ....slit it down the side 
>and  place over the steel line as an insulator.....

Near as I can tell, my fuel line is pretty well isolated from the engine 
block and other parts; and it is on the opposite side of the engine from 
the exhaus manifold.


>another thing to look for is a piece of trash in the fuel line that acts 
>like a check valve..... maybe in the tank....it gets pulled into the  end 
>of the line and stops the fuel flow....but when the fuel pump quits 
>suckin.... it falls back out into the tank.....the ignition coil  could be 
>breaking down with heat too....

Two more things to look into...

>- - - - - - - -
>
>From: FARMALLM@aol.com
>
>
>I have experienced simular problems with my 55.1.  I discovered that the
>problem was crud in the old gas tank, dirt, rust, small plastic toys etc:  My
>solution, until can get the tank out and clean it.  Carry a lenth of rubber
>fuel line connected to a short piece of metal fuel tubing. When it conks out.
>  Connect the tubing to the fuel line before the filter and blow the crud out
>of the fuel pick up tube in the tank. Reconnect fuel line to the filter and
>drive on. For a better long term solution I'll clean and seal the tank in the
>spring.

This "crud in the gas tank/fuel line" is gaining credibility, isn't it?

>- - - - - - - - -
>
>From: Bruce Damen <little-castle-contracting@cadvision.com>
>
>my understanding of vapor lock is that if you have a none venting gas cap on a
>gas tank that needs a vented gas cap you basiclly cause a vacum in the gas 
>tank
>and the fuel pump is unable to suck any more fuel.....   thats my version.


OK, OK, I'm gonna get a vented gas cap, regardless...


>- - - - - - - - -
>
>From: "john r dorsey" <jrdorsey@strato.net> 5.0
>
>
>You probably have a clogging pick up filter in the tank. I've seen this many
>many times.
>
>
>There are three cures, the good, the bad, and the ugly.
>
>The Good: Pull the tank, clean it, replace the pick up "sock" filter, enjoy
>many years of trouble free service!
>
>The Bad: Drain the tank, put a few gallons back in, drain the tank, put a
>few gallons back in, etc, etc, until you stop getting trash out when you
>drain it. This does not always cure the problem.
I'm not sure I have the skill or equipment necessary to, as you say "pull 
the tank," but I guess I can look into that..


>The Ugly: Take the line loose at the fuel pump, REMOVE THE GAS CAP, take an
>air hose and blow it into the fuel line. You should hear a thump then air
>escaping from the tank filler. You have blown the filter off the end of the
>pickup tube. You MUST put an inline filter btween the tank and the fuel pump
>or all the trash will end up in the pump.

Thank god I've got a mechanic...



>- - - - - - - - -
>
>From: "REBUS-KNEBUS" <REBUS-KNEBUS@email.msn.com>
>
>To prevent vapor lock, use clothes pins (minimum of 5 along the fuel line
>from the fuel pump to the carb, they will draw the heat from the line.  If
>this is truly vapor lock this should solve the problem.
>
>- - - - - - - - -
>
>From: "dorson" <dorson@netins.net>
>
>Howdy,i have a 58 apache and a couple times when i first got it i had 
>similar trouble,and i found that all the juice to run things has to go 
>through the amp meter and mine had a loooooose connection.Once it quit at 
>a stop light and as i cranked and cranked it wouldnt start ,anxious people 
>behind me,i reached under the dash and "adjusted"the connection to the amp 
>gage and it popped right off.I tightened the connection and have since had 
>no trouble and it is 100 mile a day roundtrip to work  and yes it fires 
>right up at 20 below zero.
>
>
>- - - - - - - - -
>
>From: "Brad Pace" <britclas@ior.com>
>
>
>Hello Paul, My 46 GMC would do the same thing and It was finally traced to 
>a bad condensor. Although I have also seen similar symptoms from a bad 
>coil. Good luck, Brad



Well, there you have it... quite a cross-section of possibilities.

Thanks again to everybody who wrote...

--PS




***************************************
Paul Schatzkin, aka The Perfesser
General Manager, songs.com unit of Gaylord Digital
shipping - 3927 Cambridge Ave #2 Nashville TN  37205
mail: P.O. Box 121616 Nashville TN 37212
ph:  615-298-1122 - fax: 615-298-4825
e-mail: perfessr@songs.com
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