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Vapor Lock?

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New User

Apr 27, 2009, 2:25 PM

Post #1 of 4 (1123 views)
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I've got a 51 Chevy p/u with a 283, 4 bbl. It starts fine when cold and runs great. Engine temp on the highway is a little below 180 and it rises a little in stop and go traffic. When stopping somewhere and turning it off and allowing it to sit for a few minutes it will turn over but not start. I checked for voltage at plug one with a spark plug tester and compared the light intensity inside the tester with when it is running and it looks ok. There is a fuel filter, in a clear housing, between the fuel pump and the carb and when it wouldn't start the other day I noticed it was empty, when cold it's almost completely full. If allowed to sit awhile it has to be cranked some but will start and run fine. I ran it yesterday and took it home before turning it off and had the same trouble. This time I didn't start it but let it sit and watched the fuel filter. After about 30 minutes fuel slowly started appearing in the filter and a few hours later it was pretty full again. Also for what it's worth the gas tank is in the cab behind the seat so it is above the fuel pump. Isn't there a valve in this mechanical fuel pump that should prevent gas from running back through it towards the tank? Any ideas? Thanks!

Hammer Time
Ultimate Carjunky / Moderator

Apr 27, 2009, 2:39 PM

Post #2 of 4 (1119 views)
Re: Vapor Lock? [In reply to] Sign In

A vapor lock is entirely possible but you should be able to see if the fuel line passes close enough to a heat source to cause that. If so, you just need to insulate or move it away from the heat source.

Make sure it's not the carb needle that is doing the leaking and the fuel is flowing into the engine. A common problem on these older carb engines is the rubber fuel line going to the tank getting rotten and porous. Mechanical fuel pumps are designed to pull as opposed the electric pumps that are designed to push. If the rubber hose gets porous, it will not only leak fuel out but it will suck air instead of fuel when the pump tries to fill the lines again.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

New User

Apr 27, 2009, 2:52 PM

Post #3 of 4 (1115 views)
Re: Vapor Lock? [In reply to] Sign In

This truck was rebuilt, took almost 3 years, and completed last November. The metal fuel line from the tank to the pump, fuel pump, carburetor, like a lot of other things on this big ol' money pit are all new. The fuel line from the pump to the filter is rubber hose. The line on the output of the filter is rubber hose to within 6 inches of the carb where it is metal. These fuel lines and the filter are all very close to the engine. I'll try insulating them. Guess I could pull the air cleaner after shutting it off to see if gas is seeping into the carb too. and don't get me wrong about the money pit crack. There's nothing like cruising through town in it.

Hammer Time
Ultimate Carjunky / Moderator

Apr 27, 2009, 3:02 PM

Post #4 of 4 (1112 views)
Re: Vapor Lock? [In reply to] Sign In

You can experiment a little by pinching off the rubber lines at one side of the filter or the other to see if either restriction isolates the bleed down. Then you will know what direction to work on.

Look for places where the fuel line passes too close to exhaust. The block itself wouldn't be hot enough.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

(This post was edited by Hammer Time on Apr 27, 2009, 3:04 PM)

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