Vapor Lock Return Line

I haven't had this Willys but a little over a year now. Among a lot of annoying issues I'm sorting out, vapor lock is one of them. This vehicle is a M38 with a 225 and a Holley 390 which I can't seem to recall the model off the top of my head right now. It has an electric fuel pump to the rear of the vehicle

I will be installing a new radiator, shroud and possibly electric fans shortly (it over heats at idle) and relocating the fuel filter and Holley pressure regulator which is currently bolted to the intake manifold and getting heat soaked badly. I'm also installing a pressure gauge on the opposite end of the pressure regulator to verify I have sufficient pressure from the pump. I keep hearing that I need to have a return fuel line to help keep cool fuel circulating.

I've tried and tried to find pics and diagrams showing the return and how it should be hooked up in the engine compartment area, but can't find anything that I think applies. I did find a return fuel line going back to my under seat tank, but the other end is connected to the carb at where I think is normally suppose to be the charcoal canister port connection.

I would think a return connection should be as close to the carb as possible (but not connected to the carb) and have a much smaller return line so that the pump doesn't run full bore and still keep enough pressure to supply the carb. What am I missing and am I over thinking this?

BTW, I log in almost every single day to read the latest info and going on's even though I don't respond much. So I just want to say THANKS, I appreciate all the generous knowledge you all give out so graciously every day.

 

Holley makes a fuel pressure regulator with a bypass fuel return port. The rest is just plumbing. PN 12-803BP. You should mount this as close to the carb as possible.

 

The original return line on a v6 cj5 was from the mechanical fuel pump back to the tank. A Holley 8007 doesn't have a return line on it if that is what you are running. The overheating at idle is most likely another problem. A 225 is very easy to cool. If a decent radiator and a 180 thermostat are present, it should cool without issues. An electric fan, like an electric fuel pump just adds one more independent system into the equation. You already need to turn the water pump and alternator so why not just let the fan spin along too? I would double check your timing also as too much timing advance can cause heat also.

 

I already have that Holley pressure regulator, so I'll just plumb the other end for my return. (Thanks) I'm guessing the small return line is the correct size so as to not tax the fuel pump excessively? And it is already right next to the carb and I was going to move it onto the firewall. Now I'm thinking I should just insulate/isolate the metal to metal with a piece of phenol block.

I agree on the over heating issues. I took the radiator in to have it rodded out, but when I went to pick it up at the shop they only did a pressure and flow test and said it was good. I mentioned that I did not have a shroud and they said I don't need one, but I already know that's one of my biggest issues. I replaced the stat with a 180 deg. when I did the radiator. Just thought while I was at it I would fabricate a shroud starting with a new radiator.

Seems like a lot of talk about using electric fans, but I agree to the old KISS method (keep it simple stupid) and I have lost an alternator which would pretty much shut me down real quick. I haven't checked the timing yet, but that will be top on the list. Thanks!

 

I have a 225 in my CJ2A. I had the return line capped off on the fuel pump. Vapor locked all the time. Hooked up the return to the tank and problem solved.

 

Well, I should have listened to Daryl and ditched the electric fuel pump and went with the mechanical. I didn't have the correct Holley bypass regulator so I bought one and plumbed it in. My M38 tank was at some time re-sealed with an unknown internal liner that was done without taking the bottom drain plug out, which ended up ripping and twisting the liner when I removed the plug. Those tanks are spendy, but it would have happened whether electrical or mechanical pump.

It had run great so far, but I had only taken it a few miles from home. The real test was to drive it on a hot day, so I drove it 35 miles this past week to work and back. Dam if it didn't vapor lock again, but when I pulled the fuel line to bleed out the pressure, the pump still wouldn't run. The existing pump has no markings on it and I suspect it's a cheap brand. I climbed under and grabbed the pump and it was screaming hot. I'm thinking it is over worked, especially with the return line. It would start moving fuel as it cooled, but barely. I let it sit over night and once again moved fuel as it should.

Should electric fuel pumps (quality brands) be up to the task of running continuously at full bore. I looked at a Carter fuel pump at NAPA today and it was huge compared to what is under there now. I'm tempted to pull everything out and just run the mechanical, but I' hell bent on making this work.