My 400 likes to vapor lock right in the very last part of metal line headed for the fuel pump. I checked and fuel delivery plentiful, pours out of line from tank, and if I pour water on that little 2 foot long stretch of line, she takes right off. The manifold is not really very close to that line, but theheat radiates over to it and heats it up. I wrapped it in rubber fuel line then heater hose over the top of that and problem is probably 50% of what it was, but still a problem. Next is wrap the line in header insulation and if that doesn't work, a new bigger fuel line from tank solenoid and routed away from exhaust, but an inline electric would be the easy fix, just looking for ideas.

 

The fuel line on mine runs about an 1" from one of my header ports as it crosses over the frame to the fuel pump and I don't have an issue. I have had, historically, vapor issues from the pump to the carb (not before the pump). What's your line from the pump to the carb? original metal line or something else? Wondering if that's not moving the fuel fast enough and it's "pooling" behind the pump and heating up.

Electric fuel pump fixes all as it'll push the vapor up through the carb so it doesn't give you trouble.

 

its the original metal line. That might be contributing to the issue as well, I am going to test pump with gauge and see if there is any pressure at all when condition persists, but it needs to be a warm day for it to even give trouble. I notice you are in TX, low elevation, I am at 6000' and uphere gas boils pretty easily.

 

good observation on the elevation! I think an electric fuel pump might be your best option then.

 

thanks for the reply, The metal line is an easy test. On boats that vapor lock, merc marine recommends larger fuel line to help the problem. It works too. more gas means harder to boil, less suction so boiling point rises, and larger diameter so absorbs more heat.

 

I seemed to have the contrary - I had a couple '78s before that had rubber (and larger diameter) lines between Pump and Carb (routed the same path) and the gas would boil. When I went to a smaller (metal or rubber) line the vapor lock issue went away. (2nd time I had this issue I also had an electric fuel pump on it - before I changed to smaller diameter line I could only drive a mile or two before I had to turn the electric pump on. After switching to smaller diameter line between pump and carb I no longer needed to turn electric pump on. Seemed like the smaller line kept the fuel moving fast enough it didn't have time to heat up... aces I guess.

 

I think so on pressure lines this is true, on suction the opposite is true, more pressure means higher boiling point, vacuum means lower boiling point, so that would make sense that a smaller metal line would be less apt to boil.

 

Wrap that part of the line 1st in self adhesive a/c duct work foil tape. Then put the the rubber hose over that and then more foil tape. That will help deflect the heat. An dit cheap.

Wrap and reroute the solid line to front of block/to the right of the water pump, and if you have boil issues at the carb get a 1"phenolic carb spacer.

Carburetor Spacers | JEGS

 

I had vapor lock on hot summer days on my 460, steel 5/16 pump supply line. I am usually around 4500 feet elevation. I sleeved it with this stuff and it cured it. I forget what size I used but it was big enough that it was a 5 minute job to push it over the line down to the pump and trim it off.

https://www.mcmaster.com/#standard-w...eving/=178og1g

Its silicone coated fiberglass sleeving.

 

I forgot the old wooden cloths line (2) trick. Clamp two on there, suppose to stop vapor lock.

https://www.ford-trucks.com/forums/8...fuel-line.html

 

cool thanks. I think the line from the pump to carb are ok, so far. We will see in summer.

 

The fix for me was an electric fuel pump mounted low and in the rear where it is cool. A little bit of pressure in the hot parts of the line around the engine takes care of it. Boiling stops.

Also after hot shutdown and heat soak the electric pump will push liquid fuel to the carb so it re-starts.

 

I think there's something to that as all my trucks had 3/8" into the fuel pump and 5/16" from the pump to the carb. Even the Holley fuel fitting was for 5/16" hose.

I installed an electric fuel pump and the problems cleared up. The truck now starts like it's EFI!

https://www.ford-trucks.com/forums/1...-the-79-a.html