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Old 03-16-2003, 03:34 PM
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Talking VAPOR LOCK

I had my 1954 Chrysler six cylinder, six volt out today for some sun shine. I let it run while I put some gas in tank. When I got home it stalled and VAPOR LOCKED. I had to wait about 40 minutes before it would start?? Any suggestion about eliminating this problem?? THANKS DAVE

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Old 03-16-2003, 03:54 PM
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Vapor locking occurs in the fuel lines when they get hot, usually because they are too close to a heat source like the block or manifolds. follow the fuel lines as they looped around the engine. Once you find a spot that could be too close for comfort, reroute it if you can. Otherwise, some sort of heat shield will help. A good one, although not very good looking, is the SHINY side of aluminum foil. Just wrap the fuel line in it and see if it helps.Vapor lock occurs when the vapor pressure of the fuel is higher than the surrounding environment. In older vehicles, with "sucking" fuel pumps close to the engine, the pressure in the fuel line to the tank is reduced by the sucking action of the fuel pump drawing fuel form a fuel tank nearly ten feet away, and when heated, the gasoline may actually boil creating a vapor of gasoline which the fuel pump cannot handle, thus the name "vapor lock"; i.e. it occurs when the fuel pump, which is designed to pump liquid, loses suction as it tries to pump fuel vapour. If a hot engine won't start, all you can do is let it sit and cool off. You should check the cooling system to see if anything is causing the engine to run unusually hot (a bad thermostat or cooling fan, for example). Switching brands of gasoline may also help
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Old 03-16-2003, 04:07 PM
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I don't know if this will be of benefit but here goes. I fought with my Oldsmobile's vapor lock problem for years. Believe me, I tried everything. I rebuilt the carb and tried other carbs. I installed a wood carb spacer and a sheetmetal spacer under the carb. I tried different mechanical fuel pumps and even wrapped the fuel line with expensive aircraft insulating wrap. I also had the factory 1/4" return fuel line in proper working order. Nothing seemed to help until I put a simple and very cheap electric fuel pump on the outlet of the fuel tank fuel line. I also kept the mechanical fuel pump installed on the engine. The idea was that the electric pump would "push" fuel up to the mechanical pump. That system Has been installed for about three years now and I have not had one case of vapor lock. Before that I was almost afraid to drive the auto during the Summer. I don't even think about it any more! Good luck
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Old 03-16-2003, 04:26 PM
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Winter fuel has a much lower vaporization point compared to summer, I've heard that a litre of toluene or a can of octane boost helps by adding a heavier distillation fraction to the fuel which might help the situation. I have never tried this but it seems to make sense. I have also heard adding automatic trans oil to the fuel helps too.

Try at your own risk.
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Old 03-17-2003, 08:21 AM
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Instead of adding automatic trans oil try Marvel Mystery Oil. Its made for gas motors and also cleans the inside carbon deposits, stops spark knock. I use it with 93 octane running at 11.75:1 without any problem.
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Old 03-17-2003, 10:58 AM
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Lightbulb

One other thing to consider is your coil. A coil going bad can intermittently fail with symptoms very much like vapor lock (won't start when hot or stalls and won't start once it gets to operating temp).

I had one do that on a BBC and it took months to finally figure it out. Installed a new coil and problem solved. If your motor has not had this problem in the past and you haven't changed anything, I would take a close look at the coil just to make sure. They're cheap enough.

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