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EFV-8 Club Forum / General Ford Discussion / Vapor lock

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Posted By Discussion Topic: Vapor lock     cwells 07-03-2011 @ 6:27 AM reply profile send p.m. Member Posts: 1 Joined: Jul 2011 I had big time vapor lock on my 35 while driving it yesterday. It was 100 degrees and I would not have made it home without the assistance of the inline electric fuel pump. I plan on insulating the fuel line or making a heat shield to try solve or reduce this probelm. Can anyone tell me where the fuel is actually vaporizing. Is it in the fuel line before it goes into the fule pump or between the fuel pump and the carburator? supereal 07-03-2011 @ 10:42 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 "Vapor lock" is often blamed for stalling or poor performance but, in actuality, is fairly rare. It occurs when a portion of the fuel system is too close to a heat source such as an exhaust manifold, etc. This causes the fuel to vaporize, preventing the fuel pump from delivering fuel, as you probably already know. More often, it is due to a restriction in the fuel line between the tank and the carb, or a failing ignition coil or condenser due to heat. My '47 began to have spells of "bucking", and when I turned on my electric primer pump, it smoothed out. I knew my tank was OK, as it was new, as was most of the fuel system, including the mechanical pump, and the ignition system was in top shape, too. Finally, the car stalled altogether out on the road. As I have related here before, I found that the fuel line between the electric pump and the firewall was mostly plugged due to rust and dirt, and we couldn't even force a wire thru the line. In 60 years of working on old Fords, I hadn't seen any bad fuel lines, so I had assumed, wrongly, that the problem wasn't there. So much for being sure. A $20 fuel line and an hour's work did the job when the elctric pump could no longer force fuel thru the clogs. The quarter inch copper coated steel line is just big enough to provide an adequate flow, and any obstruction will result in problems. TomO 07-03-2011 @ 10:50 AM reply profile send p.m. Senior Posts: 7264 Joined: Oct 2009 If your pump is producing at least 2 lbs of pressure, you probably do not have vapor lock. If is not producing the minimum pressure, replace the pump or have it rebuilt if you have a show car. Your problem could be a restricted line on the input side as Supereal stated. This could be the line from the tank or the flex line leading to the carburetor. It could also be the pickup line in the tank or a connection that is leaking vacuum. Tom supereal 07-03-2011 @ 3:40 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 When checking fuel pressure, also check volume. You can have plenty of pressure, but insufficient delivery. That is what misled me with my '47. Bill Wright 07-03-2011 @ 7:22 PM reply profile send p.m. Member Posts: 49 Joined: Oct 2009 I understand the volume/pressure part of the vapor lock cause theory. But doesn't Altitude and Ambient daytime temperature play a role in vapor lock? Don't Believe Everything You Think! Bill Wright Stroker 07-03-2011 @ 8:29 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 Bill: One also has to consider the Reid vapor pressure index of the fuel. "Winter" gas for example is blended to be more volatile, and "Summer" gas conversely is blended with a lower vapor pressure. If you filled up in the early Spring, you might have a big dose of "Winter" gas. Bill Wright 07-03-2011 @ 9:09 PM reply profile send p.m. Member Posts: 49 Joined: Oct 2009 The reason I ask is my '37 runs OK at sea level on 80-90 degree days. I have had problems at 5-7 thousand feet above sea level on 80-90 degree days.If I pull the hood sides off and run without them the problem disappears. Don't Believe Everything You Think! Bill Wright supereal 07-04-2011 @ 11:59 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 You may have a combination of problems, in that case. The delivery of fuel to the carb may be low, and "heat soak" may be boiling away the gas in the carb bowl at high ambient temps and demand.. The carb doesn't hold much fuel. By the time the float is in place, then even less. If you are satisfied that the volume of the flow is sufficient, you can lessen heat soak by covering the exhaust holes under the intake manifold, and adding a couple of extra carb base gaskets. We used to use pennies for the riser plugs. Very seldom is a problem with an old car caused by just one thing. A deficiency in one area often shows up as a problem in another location, making accurate diagnosis tricky. That is why we emphasize finding the cause of a problem before starting to change things. "Vapor lock" is often a convenient excuse for trouble elsewhere. MG 07-04-2011 @ 12:36 PM reply profile send p.m. Senior Posts: 1262 Joined: Nov 2009 "Vapor lock" is often a convenient excuse for trouble elsewhere." - Profound!

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