I am trying the vapor lock solution that was suggested by Michael Morton a while back. Like him, I had my Q-jet filter housing modified with a return line outlet at the top of the housing. My mechanic drilled, tapped, and soldered in a fitting to attach a return line to the gasoline filler pipe. I then had him tap into the filler pipe and run the line for me. I would have done that part myself but for having wrist surgery about 6 weeks ago making me unable to use my right hand fully.

The theory is the same as using the three port mechanical fuel pump or a three port filter, but it eliminates any deadhead all the way to the carb. Michael said this was the thing that FINALLY cured his vapor lock issue. I'm hoping for the same results, having tried everything else, but in tank pumps.

Pics at: http://www.gmcmhphotos.com/photos/g6819-carburetor-fuel-return.html

Carl S. wrote on Fri, 10 July 2015 18:04

I am trying the vapor lock solution that was suggested by Michael Morton a while back. Like him, I had my Q-jet filter housing modified with a return line outlet at the top of the housing. My mechanic drilled, tapped, and soldered in a fitting to attach a return line to the gasoline filler pipe. I then had him tap into the filler pipe and run the line for me. I would have done that part myself but for having wrist surgery about 6 weeks ago making me unable to use my right hand fully.

The theory is the same as using the three port mechanical fuel pump or a three port filter, but it eliminates any deadhead all the way to the carb. Michael said this was the thing that FINALLY cured his vapor lock issue. I'm hoping for the same results, having tried everything else, but in tank pumps.

Pics at: http://www.gmcmhphotos.com/photos/g6819-carburetor-fuel-return.html

Carl. I'm very interested in this mod and have all the parts ready to go. I just returned from a trip to Huntington Beach and had some vapor lock at 110 F until i activated the electric pump--nothing serious but I would like to eliminate the need for a booster pump at all.

I don't understand how the port in the fuel filter works.
Is there a pressure regulator ( or restriction) on it so the carb gets it's 3-5 psi fuel?
Otherwise it seems you will starve the carb

Bob and Carl, I have some theories about what is happening when we suffer from "vapor lock" and I would like your opinions.

I think we should divide the fuel system into before the pump and after the pump to understand what is happening and what we can do about it. The common factor is fuel temperature - in both cases the fuel is hot, only the heat sources are different. The other factor - the one that varies - is "atmospheric" pressure. Before the pump we have whatever pressure is in the tanks minus the negative pressure from the fuel pump - a bad combination in that part of the system can cause the fuel to boil in the tanks and/or the lines causing the pump to lose its prime at least momentarily if not longer - I think this is where the term "vapor lock" came from. The farther away the pump is from the tanks the more chance there is for this to happen because more vacuum is required. After the pump the fuel is under more pressure and is much less likely to boil but the heat added getting to the carburetor can still be enough to cause some "stumbling" but probably not stalling under most circumstances since the pump continues to apply pressure and the bubbles quickly go away.

An electric fuel pump installed near the tanks requires less vacuum because it is closer and below the tanks so it helps eliminate the pre-pump vapor issues. The electric fuel pump's added pressure helps prevent vaporization after it. The three-port fuel filter at the carburetor combined with some in-tank pumps would seem to be the best solution.

The 3 port filters and fuel pumps have restrictions. They do NOT flow full 1/4 inch. Check out the following picture and description.


http://www.gmcmhphotos.com/photos/3-port-fuel-pump-2c-filter-2c-and-hot-fuel/p41489-3-port-fuel-pump.html

I think this is where the term "vapor lock" came from. The farther away the pump is from the tanks the more chance there is for this to happen because more vacuum is required. After the pump the fuel is under more pressure and is much less likely to boil but the heat added getting to the carburetor can still be enough to cause some "stumbling" but probably not stalling under most circumstances since the pump continues to apply pressure and the bubbles quickly go away.

An electric fuel pump installed near the tanks requires less vacuum because it is closer and below the tanks so it helps eliminate the pre-pump vapor issues. The electric fuel pump's added pressure helps prevent vaporization after it. The three-port fuel filter at the carburetor combined with some in-tank pumps would seem to be the best solution.