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If two 3 port valves are used use one 3 port switch. Since the valves default to the rear tank hook the return for for the rear to the rear port of the second 3 port valve and the return for the front tank to the front tank port. Then jumper the 12v input to the first three port valve over to the second three port valve. Uses 1 switch to call both valves. Run the return line to the second 3 port output, but now the input port. Yes I do think it would be doable like that.
For electric impeller type pumps it may be counterintuitive, but when they are running free they are turning more and using more power than you think. When pushing against some pressure it can slow down the motor making less load on the system. That in and of itself might not be a reason to add a return. What kind of electric pump are you using?
A good reason to have a return is to prevent vapor lock, but then a midship low on the frame epump is good insurance for that.
If your pump produces more pressure and volume than needed a return could aleviate a flooding issue by overwhelming a carb designed for 4 to 6 psi.
At the moment I'm just running one of those little crummy edelbrock electric pump that puts out about 4-6 psi but i want to put a holley pump in with makes about 10 so I'd need to regulate it anyway
So the engine is out of a EFI truck ? Can't you find a EFI truck and mirror that fuel system ?
On my 86 302EFI, the return line is 5/16.
I assume you Gary's site where you can see the 86 EFI set up ?
I'd have to change a lot of wiring and plumbing to use the efi system and then I'd have have about 35 psi to much for the edelbrock i have supplying fuel
Is the engine still EFI, including all of the electronics, etc.? Or did you swap over the intake and carb from the pre-EFI engine and now there's no provision for a mechanical pump?
Reading between the lines, I think you mean the latter but want to be sure.
I work my 351W truck VERY hard in the summer, hauling a slide-in camper in hot weather. I had LOTS of problems with heat affecting the fuel, as detailed at the link above. I converted to full electric, with no return line, and kept the stock 3-port fuel switching problem. Zero problems since then.
The only other major modification I made was to block off the exhaust crossover passage in the stock intake manifold.
For dealing with heat affecting the fuel, aka "Vapor Lock", keep in mind there are two aspects to the problem. For best results, you'll want to address both issues. Lots of good details in this thread:
OE parts will be copying a 460 fuel system which does use in tank pumps.
If you do not mind putting a return line in the tank itself, that would be the way to go. If you want a safer way to put a return line in place on both tanks, you could take the metal filler neck off and modify it on the bench to accept a fuel fitting and let the return fuel run down the filler neck hole.
For the return part of it at the carb, I would run one of these aftermarket fuel filters that has 3 ports. Chryslers used these alot.
I think i would prefer for the return to go directly into the tank. Minimize the chance of fuel sloshing out. I'll probably drop the tanks and I've seen kits online to add a return so I'll just use one of those. I've never seen that style filter before does it act as a pressure regulator?
I think i would prefer for the return to go directly into the tank. Minimize the chance of fuel sloshing out. I'll probably drop the tanks and I've seen kits online to add a return so I'll just use one of those. I've never seen that style filter before does it act as a pressure regulator?
You would use that 3 port filter just before the carb and it would go into the 2nd 3 port "return" valve as it would pick what tank the return fuel goes to.
The hardest part I see is how to plumb the return in at each tank?
BTW that 3 port filter the return has to be at the top or the fuel will not get to the carb.
Dave ----
I think i would prefer for the return to go directly into the tank. Minimize the chance of fuel sloshing out. I'll probably drop the tanks and I've seen kits online to add a return so I'll just use one of those. I've never seen that style filter before does it act as a pressure regulator?
That filter has a sized return to return a portion of the fuel to the tank. Like the 460's used, a fixed orifice. It does not regulate. If you are going to use that higher pressure fuel pump, then use a 3 port regulator like you mentioned.
You would use that 3 port filter just before the carb and it would go into the 2nd 3 port "return" valve as it would pick what tank the return fuel goes to.
The hardest part I see is how to plumb the return in at each tank?
BTW that 3 port filter the return has to be at the top or the fuel will not get to the carb.
Dave ----
There are fittings like the one below where one just has to drill a hole into the tank and then tighten this into the hole. Or as previously mentioned on can put a port onto the fuel filler neck. But then i worry about fuel finding it's way out of the cap side
You can change your sending unit out for one with a return line incorporated into it. That's what I have for my diesel fuel return. I think the diesel sending units have everything you need and would be plug and play.
That isa bulkhead fitting, yes that is how it's designed to be used, but you might want a silicone gasket for it, you can make one up from a piece of silicone.
Here's the lines on my 86 EFI tank.
I used a piece of silicone to seal a leak in the return line.
Have you actually had any heat-related problems with the fuel system? In my over-inflated opinion, converting to an electric pump (near the tanks) and running a quality low-octane fuel* will probably take of the problem. Seems like adding a return system is a lot of work with very little to be gained. From my own experience, just those two things alone took care of it.
I echoed what Karl says above. What set up are you using now that's causing your issue? I'm assuming it's vapor lock. Use an electric pump sized for your carb and that has solved any vapor lock reported here. You say it's hot where you live. That can cause issues. Anyway be sure to post what you end up doing and how it works for you.
Have you actually had any heat-related problems with the fuel system? In my over-inflated opinion, converting to an electric pump (near the tanks) and running a quality low-octane fuel* will probably take of the problem. Seems like adding a return system is a lot of work with very little to be gained. From my own experience, just those two things alone took care of it.
i get vapor lock during the summer pretty consistently. i'm probably overdoing this but i like to be over prepared. i'll look into better fuel stations here but montana has pretty consistently bad fuel
I echoed what Karl says above. What set up are you using now that's causing your issue? I'm assuming it's vapor lock. Use an electric pump sized for your carb and that has solved any vapor lock reported here. You say it's hot where you live. That can cause issues. Anyway be sure to post what you end up doing and how it works for you.
i have an edelbrock fuel pump feeding my avs2 and it works pretty well accept for hot starting. part of it is probably in my tuning but during the winter months i'm able to fix it so heat is definitely a factor. and the way i figure if i'm going to upgrade the system i'd rather not have to take it back apart so i'm gonna try to over build it
i figure if i'm going to upgrade the system i'd rather not have to take it back apart so i'm gonna try to over build it
How far apart is everything? Seems like a lot of work to physically add the return line. If the bed and tanks are off, access wouldn’t be too hard. But if those are presently installed, access would be miserable.
What I’m getting at is you could do the project in stages and see what happens. Given the chance to spend your time and money, I’d start with an electric pump back by the tanks. That should take care of any problems in the delivery line. I’d also add a phenolic spacer under the carb. That should help with the hot restart problem.
If the problem continues, you could always plumb the return line later. If you’ve really got your heart set on that, have at it. But if the bed and tanks are still installed (with no other reason to remove them), I’d be hard pressed to do all that extra work for minimal gain at best.
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