1980 Travel World w/454 Keeps Vapor Locking (I think)

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travelworld

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Jun 2, 2015
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Having trouble with a 1980 RV with a 454 vapor locking, I've done everything I can think of, and it's still doing this. It ran all day 70-75MPH, pulling a trailer over hills, no trouble, then all the sudden, it decided it was going to vapor lock and sputtered for 45 minutes all the way back home.  It only has 62K miles on it, and it was garage kept and well cared for.

Here's what I've tried so far:
New electric fuel pump and fuel filters, moved down and away from the heat source (the exhaust)
Moved the dual exhaust to one side (opposite the fuel lines) and installed two new high air flow mufflers
Added electric fan in front of the radiator
New plugs, wires, rotor, cap, coil, and modular
New Non-Collapsible Rubber fuel lines
Removed the snorkel, and maybe a few other things, but I'm ready to pull my hair out.

Any advice???
 
While you were in the distributor, did you happen to check the bushings on the distributor shaft? Those old distributors were notorious for giving misfire problems when the bushings get sloppy. And yes it seemed sometimes it would happen all at once.
 
How far from the tank is your electric fuel pump?  This is key as too far away from the tank and the benefits are negated, you want to pressurize the lines starting as close to the tank as possible as this pressure is what raises the boiling point of the fuel.

There was a TSB out from GM many years ago on these and I did the update on my 1984 30' Travelcraft on GM P32 chassis and she never missed a beat.  I placed my electric fuel pump right at the tank where the lines came from the tank to the frame rail, estimated about 2-3 feet from where it entered the tank.  I also kept my mechanical fuel pump in place as well.  The electric was just a lift pump to supply the mechanical pump.

I too had a free flowing exhaust with Doug Thorley Tri-Y headers feeding from two 2.5" pipes through a single high flow Atlas muffler to a single 3" outlet.  I had recurved the distributor as well as spent some time fine tuning the carburetor.  I also had a Gear Vendors overdrive unit installed behind the transmission and towed a 24' enclosed trailer to the race track and dunes regularly and this setup ran perfectly for 45k+ miles and 6 years we traveled with it.

Mike.
 
It has been long enough that memory is a little foggy, but my 1990 Winnie with 454 had a similar problem, ran OK until pushed a little, then would suddenly die, only to run fine as soon as I backed off the throttle.

The problem was the fuel pump relay which drove the electric pump, located on drivers side of radiator frame in a location accessible only by greasing my arm. (that I remember well)

Replaced it and never a problem again.
 
70-75 mph in a motorhome is going to make the exhaust headers on the old 454 get really hot. Not to mention sucking fuel like crazy. Try slowing down and maybe the problem will disappear?

I can't think of anything you haven't done, except maybe insulate the fuel lines in the engine compartment. Vapor lock can happen right in the carb, though. Maybe change over to a throttle body injection system? Not too expensive or difficult, from what I read. You could even go for port injection if you want to spend the $.
 
Here are some things that come to mind,
Cracked fuel hoses from the tank pick up. The in tank sock, tank vent, or water in the system?
 
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