1948 ->257 L8 Vapor Lock

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July 14th, 2014, 07:29 AM

roberer

48Olds78

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Join Date: Mar 2014

Location: Albuquerque, NM

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1948 ->257 L8 Vapor Lock

My 48 Olds 78 runs perfectly, for 4 miles, then Vapor Locks and I have to handfill fuel bowl to get home. I suspect Vapor Lock. Anyone know how to eliminate this? I live in New Mexico which is around 95 degrees this time of year and I can't trust driving my car for more than or 4 miles.

I replaced the upper Fuel line between Pump and Carb to get it away from the engine but that didn't fix the problem.

Can anyone help????

July 14th, 2014, 08:03 AM

oldcutlass

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Location: Poteau, Ok

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It may be a rubber line leak before the pump or possibly at the tank. Also have you checked your fuel pressure?

July 14th, 2014, 09:47 AM

1970-W30

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Location: Gilbert, Arizona

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Make sure the gas cap is still vented, the vent could be partially plugged causing a vacuum and starving the fuel pump. Or a rubber line between the tank and pump could be collapsing starving the fuel pump.

July 14th, 2014, 10:36 AM

455man

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Location: Wichita, Ks

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I had the bottom of my fuel pump leak once. It was so hot the fuel would evaporate before I noticed it on the ground. I finally caught it.

July 14th, 2014, 01:18 PM

47 Convertible

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Location: Woodland WA

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Vapor Lock Potential Fixes

Quote:

Originally Posted by roberer

__________________________________________________ __
Ran across some of this in WiseGeek.org. The rest is experience I picked up in fifty plus years of driving.

It used to be common to remove the thermostat during the summer to try to keep cars running cooler. It could be a cheap fix or not. Or you could go to a lower temp Tstat

Cars can often be retrofitted with the newer technology that reduces the likelihood of the fuel lines overheating.

Your mechanical pump located on the hot engine block may be part of the problem. It will soak up that heat and transfer it to the fuel in its bowl raising the likelihood that it will vaporize in the line to the carburetor. On a carbureted engine like yours, for example, a low-pressure electric fuel pump can be installed near the fuel tank, which will keep the fuel moving along the lines even if it starts to heat up in the engine compartment. If you think about doing that use a pressure regulator between engine and pump and remove the mechanical pump.

Another remedy is to install an electric fan in the engine compartment. It will keep the compartment cooler as it will run at top speed when needed most at idle or slower speeds. A me chanical fan simply can't do this. as it rotates at engine speed.

Fuel lines can also be insulated to prevent the fuel from getting to the temperatures at it will vaporize. I know you said you moved the line from the pump to carb but it wouldn't hurt to insulate it with some kind of heat reflecting wrap.

Fuel can also boil out in the bowl of the carburetor due to heat transfer from the intake manifold and create a vapor. A quarter or half inch non-metallic spacer between intake and carburetor can help keep that from happening.

Good luck solving that problem.
Jerry

July 14th, 2014, 03:12 PM

Funkwagon455

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Location: Aledo, Texas

Posts: 2,386

The previous owner of my straight eight had installed a very discreet electric pump near the tank to act as a boost pump of sorts ensuring a positive pressure at all times. Living in north Texas, I have yet to encounter a vapor lock. While I prefer to alter my cars as little as practically possible from a factory configuration, I'm also a proponent of the old adage "If it ain't broke, don't fix it!" Good luck with your Olds, and kudos for keeping your eight straight.