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I got this from the newsletter of a MC that I'm in. I can't vouch for its truth, but it sounds interesting. What do the real mechanics out there think...?

"I've read several questions about hot engine starting problems on 20-year-and-older cars. The owners say they've rebuilt their carburetors and fuel systems and still have a problem. Technicians call this a "hot soak" problem. The heat of the engine boils the gasoline out of the carburetor when the engine is shut off. A guy named Bob Shultz, who was a Ford mechanic 50 years ago, says it's because gasoline today vaporizes more easily. He advises adding one ounce of light oil for every gallon of gas. I use Marvel top cylinder lubricant and this totally solved the hot engine-hard starting problem for me. Maybe there are more sophisticated ways to solve the problem, but this one is easy and it works."

Any VMFers out there willing to test this theory? I would, but, of course, I have no hard-starting problem.... /forums/images/icons/wink.gif
 

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I have heard of the vapor lock problem on some cars being related to the OEM steel line between the fuel pump and carb. Reportedly better to use a rubber line if possible due to its insulation properties.

Is he referring to the infamous Marvel's Mystery Oil? I don't know about that fix.....
 

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Makes sense to me. I heard it called "Heat Soak" This happens to me when I am in Reno during HAN. I now use a insulation on my steel fuel line to the carb. I also use Marvel Mystery Oil. No problems so far. I am not sure about the light oil but Mystery Oil is about the same.
 

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Interesting about the fuel lines-my old truck vapor locked a time or two and the mechanic I use had me switch to a metal fuel line from the rubber one I was using. Haven't vapor locked since (only been a couple of months though).

J. Boggs
 

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This phenomenum is absolutely true - and something MOPAR folks have known about for a long time.

The reason MOPAR guys are most familiar with the problem is that their cars have long used Carter AFB (same as Edelbrock) carbs that came without any kind of insulating spacer and whose fuel bowls dont have the advantage of hanging out in the wind like a Holley or 4100 does. On a hot day, I can shut off my Dart GT convertible, pull off the air horn on the AFB, and watch the gas boiling in the float bowl.

Because much of the boiling gas either pools in the intake or runs down into cylinders that have their intake valves open, the car is both flooded and out of gas at the same time. Makes for some very difficult restarting.

In my case this is compounded because I live at 8200 ft above sea level. If you remember your college physics, fluids boil at lower temps the higher you go...

I've used Diesel fuel (1/4 gal per fill up) in much the same way the writer recomends using Marvel, with some success. The real solution is a 1-inch phenolic spacer to insulate the carb body.
 

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67 coupe, 69 Sportsroof, 86 hatchback
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I'll agree with MrGem. I had an old Dodge PowerWagon that would "vapor-lock" or something in hot weather. Tried everything. An old-timer suggested the diesel fuel trick with a gasoline fill-up. It worked. In the summertime I always carried a jug of diesel around in the truck.
 
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