Adding return line carbureted

[MS73HD302]

I’m running a dead head regulator at 5.5 pressure and encountering vapor lock. I have wrapped the lines with heat barrier but still having the issue. I have seen where UTG adds a Wix filter to set up a return line. I have the Toms factory replacement tank as well as the aux tank. Do y’all see anything wrong with me running a return line to one of the two vent ports on the main tank?

Link of Wix filter- http://https://www.amazon.com/WIX-Filters-Complete-Line-Filter/dp/B000C9UJAA

Thank you for the help with this idea

 

[Rustytruck]

if your main tank is full and you run your aux tank where is the return fuel going to go?

 

[MS73HD302]

Out the filler neck... which would 100% happen at some point with this set up. I figured I would run the rear dry and keep non ethanol in the front tank. Not sure how quick it would drain the front tank though.

I already have the electric selector value and have considered going old school manual selector under seat for the tanks then flip the switch for the returns and gauge

 

[73azbronco]

So I have an EFI tank, with internal 65psi pump, plumbed to a bypass regulator right outside the tank, with return to tank right there, then a pressure gauge next to carb proving I have 4.5 psi. I also use a reflective heat wrap around the fuel line from the firewall to carb.

https://www.autozone.com/ignition/h...r40PSDYLTZ4XsZQREihoCxacQAvD_BwE&gclsrc=aw.ds

I then have a 1/2 inch thick phenolic spacer below the carb, and a 1/16th aluminum heat shield below the carb. No issues here in 110 degrees after an hour on freeway, directly to a gas station stop, let it sit 10 minutes to see what it would do. Started right up. I, however, was vapor locked.

 

[jckkys]

I have never had vapor lock in my '77 with a stock system, for the 45 yrs. I've been driving it. But it only gets to 115 here. I stupidly tried an inline filter between the tank and the mechanical pump. That did vapor lock. I've also seen vapor lock in large trucks with fuel lines twice as long as EBs. I would look for anything in the fuel line between the tank and the pump. That's where vapor lock occurs. EBs are less prone to vapor lock than most autos.

 

[MS73HD302]

My problems are
after heat soak the fuel pressure climbs to 11 and gas drips down the carb on the secondaries. I thought a return line would relieve this pressure in turn solving the fuel soaked throttle blades.

Also after long runs (30 minutes let’s say) the filter up by the carb is empty but once the hood is popped gas starts filling the filter to the normal 1/2 to full level which I assume could starve the engine for fuel.

I may be way off in my diag but I’ve checked and checked and checked floats they are good until the heat soak where they get overfilled. And swapped to a smaller 9 inch element from the large 14in and have a 1 inch phenolic spacer. Truck runs great and drive it almost everyday which is why I’m so concerned about the minor flood after shut down and filter emptying.

 

[jckkys]

The problem you describe isn't vapor lock. Vapor lock is fuel evaporating in the fuel line so no fuel gets to the fuel pump. It first manifests when the engine needs increased fuel during acceleration or climbing a grade. Heat soak after the engine is shut down boils the fuel both in the float bowl and in the fuel line between the pump and the carb. This is often called percolation. Ford made fuel pumps with a return line connection in the '80s. Here's one for an '87 Crown Vic;https://www.rockauto.com/en/moreinfo.php?pk=296087&cc=1438417&pt=6256&jsn=455&jsn=455

 

[73azbronco]

You may want a return pressure regulator to stop that increasing pressure, it would bleed off back to tank. I can easily see how 11psi floods the engine.

 

[hucklburry rev2]

I don't think its heat either. Can you describe your setup, what fuel pump and where, what regulator and where, what carb, etc?

My crossflow setup from Australia has a return off the carb, I have to sort it out, the guy who had it set the return, I got to figure out where he ran it and what I going to do, this weekend. Its off a mechanical pump so I don't have a regulator. Its in my 66, so I can't use that return mechanical pump, as I am running a fuel pump with vacuum pump for my wipers....

 

[kylakekevin]

Thunderhead289 on YouTube has a great carburetor return line set up and shows' how he did it and the parts he used.

 

[hucklburry rev2]

Thunderhead289 on YouTube has a great carburetor return line set up and shows' how he did it and the parts he used.

Nice. This makes sense to me.

https://www.youtube.com/watch?v=pTg3BP0-SVE

 

[MS73HD302]

^^ that’s where I got the idea for the electronic value for the return on dual tanks. That dude knows his stuff. Glad to hear it’s percolation instead of vapor lock and that fuel pump would be an easy fix.
My set up is mechanical pump, ford cast iron 4 barrel I take off a fairlane, Holley regulator (the $30 one) and Holley 1850-2. 180 thermostat that I’ve considered dropping to a 160 to possibly fix this issue. Stock fan and radiator.

 

[hucklburry rev2]

^^ that’s where I got the idea for the electronic value for the return on dual tanks. That dude knows his stuff. Glad to hear it’s percolation instead of vapor lock and that fuel pump would be an easy fix.
My set up is mechanical pump, ford cast iron 4 barrel I take off a fairlane, Holley regulator (the $30 one) and Holley 1850-2. 180 thermostat that I’ve considered dropping to a 160 to possibly fix this issue. Stock fan and radiator.

If your engine isn't overheating, stay with the 180. That is a completely different subject I think.

You are running a mechanical engine driven pump? AND a regulator?

Ditch the cheap regulator - run from the mechanical engine driven stock pump to the carb and see how she does. You should have a filter at the carb inlet.

Did you have a reason for putting the regulator in?

 

[MS73HD302]

Cools well stays between 180-190. not much traffic to deal with. The mechanical pump put out around 9 lbs if I remember correctly. That was around 4 years ago when I put the pump on it could have loosened up since then. Worth a shot trucks way too fun to leave parked for occasional use. For the record this is not an issue any other time of the year

 

[hucklburry rev2]

Cools well stays between 180-190. not much traffic to deal with. The mechanical pump put out around 9 lbs if I remember correctly. That was around 4 years ago when I put the pump on it could have loosened up since then. Worth a shot trucks way too fun to leave parked for occasional use. For the record this is not an issue any other time of the year

Its weird for sure, I suspect the $30 regulator more than anything, I don't trust them, if I needed one, I'd probably be researching the $130 ones hoping I didn't need a $230 one.

 

[blubuckaroo]

MS73HD302, I've read this a couple of times and can't find which carburetor you're using.
9PSI fuel pressure is too high. If yours is an Edelbrock carb, then it's way too high. Edelbrocks have a shorter fulcrum point on their floats. They don't handle fuel pressure well at all. Around 4 PSI is better.
Some mechanical pumps are high like that. You either need a different pump or a good regulator.

I fought carb boiling for a while too. I ended up blocking the heat riser exhaust ports in the intake manifold, and put in a 1/2" Edelbrock spacer. I also dropped the fuel level 1/16".
Some may disagree with blocking the heat riser. It does affect the running until the engine gets warmed up. I just decided that adding heat to the carb was at least part of the problem. I first blocked it with a couple pieces of .010" stainless shim stock on the intake side of the intake gasket. Now though, my aftermarket heads came with that port plugged already.

 

[MS73HD302]

It’s a Holley 600 4 barrel vacuum secondaries that I added a rear metering block for jets.

So today I removed the regulator and put a gauge between pump and carb and surprisingly the pressure is at 5 lbs. put another heat sleeve over the line from pump to carb so have two in there now and added on the line from tank to pump which solved the problem of the filter going empty.

also noticed the metal heater valve for the temp control was on the breather line going up to the air cleaner so put some wooden clothespins under it for a heater barrier. After these adjustments pressure creep still there and secondaries are still wet. Knocked one issue out so we’re definitely heading in the right direction.

I’m guessing that the regulator whooped that pump into submission because I remember before installing the regulator high fuel psi and the pressure was jumping all over the place.l where now it’s a constant 5 psi