[mrtonegto]

I'm running an orifice and a 1/4" return fuel line off of one side of my Holley deadhead regulator. It's a .035 orifice and has been working fine - no more flooding and/or pressure creep.

I'm about to install a new large canister fuel pump that has the 1/4" return line and I'm hoping I can run both the orifice and the return line off the pump.

Anyone know a way to plumb those both into the same line w/o issues?

[lust4speed]

So you will be running both an electric pusher pump and a stock type mechanical pump?

I've had to install a regulator just before the carb because total pressure increased. Many say it won't, but my installs have. I'd move the regulator and it's return after the mechanical pump, and not bother with the mechanical pump return.

[mrtonegto]

I should have been more clear............ I am only running a mechanical pump and it will be replaced with another mechanical with the larger canister and return feed.

My regulator is as you stated - after the mechanical pump.

The current pump takes waaaay to long to build pressure after the car has sat for even a day, so it's probably going to die before too long. Not to go off on a tangent, but I've considered putting in one of those small flow through electric booster pumps by the tank but that would only mask the real problem.

Wouldn't blocking the return fitting on the new pump cause it to build pressure? I'd prefer not to mess with the size of the orifice since it's working so well.

[lust4speed]

The 1/4" return fitting on the mechanical pump has a built-in restriction that usually measures out at about .067". I'll include a pic of the inside of a deep pump that shows the tube with the reduced inlet.

Have you checked the hoses back at the tank and even the length of tube along the frame rail? It doesn't take much of a leak to pull in air and really slow down the priming of the pump.

That said, I finally broke down and went with a small electric pulsating pusher pump back at the tank to avoid the long cranking periods after the car has been sitting a week or longer. It's usually okay at the three day mark, but give it a week or more and it takes awhile to get fuel up front. The electric pump is only feeding my 400 engine so I wasn't too worried about its size being too small. We have went with the Carter rotary pump along with a bypass with a check valve around the pump on the higher cubic inch engines.

[mrtonegto]

Actually yesterday I did find that I was able to twist the main braided line at it's attachment to the hard fuel line above the tank. I wondered if that could have contributed/caused some issues just as you described. I tightened it up but have not run the car as yet - working on my front suspension rebuild.

Still wondering what the issues might be in capping off the return feed on the mechanical pump......................

[lust4speed]

The mechanical pumps build pressure from spring pressure - the arm pushes the diaphragm compressing the spring and the spring pressure pushing back on the diaphragm is what gives the output pressure. The spring doesn't push any harder with the return blocked, so maximum pressure is the same either way. The bleed-off does slightly lower output pressure under high demand since it does divert some fuel flow. I'd like to say no difference, but I've read that pressure does drop slightly with the return - say from 6-1/4psi with the return capped off to maybe 6psi with it open and functioning when the engine is running.

The return line therefore causes a little loss in pump efficiency, but that is offset in bleeding off any gas vapor*. The return pickup opening is at the very top of the chamber and fumes are the first thing to be pushed out of the pump. The .067" hole would seem very large to vapor, but doesn't really return that much fuel to the tank after the vapor is purged.

You might be able to get away with plumbing the two returns together. Someone can correct me if I'm wrong, but I'm thinking that the mechanical pump return and the regulator return are being supplied by the same static pressure? If so they will get along just fine, and as long as the 1/4" return line doesn't have any restrictions, both lines together shouldn't come anywhere near the return line's flow capacity.

So while you can use both, we only use the return on the mechanical pump and a dead-head regulator with no return even with the Carter pusher pumps feeding a large RobbMc.

* And the problem with gas vapor under hot idle conditions is very little fuel is used so the supply is basically stagnant. The amount of vapor displaces liquid fuel and eventually the pump is pushing down on vapor instead of liquid and things move along pretty quickly to vapor lock and a stalled engine. At some point the pump will be only pushing vapor into the carb and the engine quits.

[pfilean]

Remember that before the mechanical pumps with the vapor return were made the solution was to have the vapor return off the filter just above the pump. Flow was vertical through the filter. The top of the filter had a chamber where the vapor takeoff was higher that the takeoff to the carbs so the vapor could separate and get pushed out. The pump didn't know or care if there was a vapor return. When the vapor return was moved to the pump (about the time some of the filters were moved closer to the carb and not sitting with the flow through vertical or they started to use the little filters at the carb inlet) the 1/4 return was still used. The vapor separator in the pump should perform the same and the pumping action won't know or care if there is a vapor return. Just run the return line to the tank. The little orifice in the pump will take care of controlling the flow and pressure will be little affected. Some people have used the vapor return pumps with the return outlet plugged and not had a problem.

Of course if you really are getting the 6+- psi mentioned then you need to consider if your carb setup can tolerate that much pressure and keep the needle in the seat. Maybe then you need a regulator. In particular the 2GC carbs are touchy on pump pressure.

[mrtonegto]

I do run a Holley dead head regulator - see above, attached to it is the .035 orifice.

My thoughts were to T the mechanical pump's return line into the current return line from the orifice. Wondered if there would be any issues with backflow, etc.

[TheSilverBuick]

I just put a cap and hose clamp on the return port of the mechanical pump on my Buick. Been that way for a few years. Since you have a regulator after the pump already, I would just cap the mechanical pumps regulator. You shouldn't get built up stagnant fuel in the mechanical pump since the holley regulator is bypassing some, or at least by-passing the vapor build up.

[Cliff R]

If you are using a Holley regulator not designed for a return, the you are just robbing some of the fuel that would normally go to the carb and routing it back to the tank. Using a .035" orifice really isn't much of a return right to start with, as it's quite a bit smaller than the needle seat assemblies in the carburetor.

The return system should be before the regulator, on the higher pressure side of the system. The reason for this is that the standard size Holley regulator has a very small orifice/check ball right to start with. It's designed to control pressure, and less pressure on either outlet means less flow. Probably not a big deal to rob a tiny bit from it, but you'd quickly run into troubles putting a bigger hole in the restrictor.

The best set-up would be to get a return style regulator, and not use the one at the pump, or the restricted orifice set-up that you are using now.....IMHO.....Cliff

[mrtonegto]

Gee, I got that orifice idea from s o m e o n e on the board...........hmmmm

Kidding aside, I realize I did add new issues with the return line and the return style pump.

The orifice works so well though so I'm leaning toward keeping it as-as and installing the new pump with it's return blocked.

Great feedback from all, thanks.

Tone

[Cliff R]

Nothing wrong with having an orifice in the return system, but the return system isn't supposed to come off the carburetor feed side of the regulator. That is robbing fuel from the carburetor at full throttle, as it will act like another carburetor is being supplied on the low pressure side of the system.

The orifice that you installed, if it is coming off one side of the standard type Holley regulator, is simply dampening "spikes" in pressure and pressure build produced by whatever type of pump you are using. I've seen this happen many times with "dead-head" systems, even if the fuel pumps being used were supposed to be able to run that way.

I use a bypass system myself with the standard Holley regulator, but there is no restrictor installed in it. I have a 3/8" "T" on the supply side of the regulator, bushed down to a 90 degree 1/4" inverted flare fitting and hooked up to the factory return line. Since the fuel has to make two right turns to supply the return line, and it's only 1/4" steel tubing, it puts enough pressure and flow to the regulator to supply all of the fuel to the carb at full throttle, then bypass back to the tank when less delivery is needed.

I installed the system with a valve in it to run "dead-head" if needed, but have never had to close the valve. It's a pretty crude system, but it works. When I tried to run "dead-head" (Comp 140 pump), after 15-20 minutes of driving the pump would start making all sorts of noise and pressure was all over the map. It burned the brushes out of my first pump in about 2 months.

After installing the bypass system, the next pump lasted over 10 years of street and track use, then started acting up. Took 5 minutes to install a new set of brushes and right back in service.......Cliff

[mrtonegto]

Your description of my system is spot on. It bleeds enough pressure from the low pressure side to have virtually stopped the issues I was having with pressure creep and flooding. Those would occur after a brief stop for BBQ and made my heartburn even worse.............

I have not noticed any ill-effects feeding the tri-power at full throttle, but I don't have any time slips to make a before/after comparison either.

If you've got a picture of your return system I'd like to see it.

[Cliff R]

Using a very small .035" hole would have it as more of a bleed off system than a return system, and I would continue to use it provided it eliminates the flooding issues and pressure fluctuations. I'll also bet that it helps to smooth out fuel flow from the mechanical pump, as they use valves that open and close vs free flowing like an electric pump.

There are no absolutes with this hobby, and more than one way to get a good end result with these things.

If you ever step up to a rear mounted high flow electric pump, large fuel lines, etc, a return system would be more in order than a bleed off system, as this really takes a LOT of load off the pump vs running them "dead-head"........Cliff

[RobbMc]

We recommend using a "bleed" or "vapor return" with our mechanical fuel pumps. The bleed should have a .030" to .040" diameter restriction. We sell a "vapor return" fitting (which already has the restriction in it) that accepts a 1/4" return line . When running one of our pumps without a regulator, we install the vapor return (VR) fitting in the outlet side of the pump. When running one of our pumps with a dead-head regulator, we install the the VR fitting in the outlet side of the regulator, rather than in the pump.

Having a VR or "bleed" not only reduces the chance of vapor lock, but it also improves hot starts because it eliminates the pressure in the fuel line as soon as you shut off the engine. Without a bleed, a mechanical pump can keep pressure against the needle and seat when the engine is not running. Fuel can then slowly leak past the needle and seat, flooding the carb. Then when you try to start the engine 20 minutes later, you have to hold the pedal to the floor to start the engine.

When running a dead-head regulator with a mechanical pump, having the bleed on the outlet side of the regulator not only reduces vapor lock and improves hot starts, it also eliminates the pressure creep that can occur with dead-head regulators.

We do not recommend running a bleed line from both the pump and the regulator. If you are using a regulator, install the bleed in the regulator and plug the one on the pump.

PS. Return (or "bypass") regulators are NOT the same thing as a dead-head regulator with a VR/bleed line. Return regulators return ALL of the unused fuel back to the tank and require a large return line (often larger than the feed line). A VR/bleed line only returns a very small amount of fuel back to the tank, even at idle, so a 1/4" return line is sufficient.
I highly recommend using a return/bypass style regulator with an electric pump. There are numerous advantages and no drawbacks (other than the need to install a large return line). However, mechanical pumps generally don't work well with return/bypass regulators (due to the pulses generated by the pump, especially at low engine speeds). So a dead-head regulator with a VR/bleed is recommended with a mechanical pump.

[dmac]

Thank you RobMC. Good explanation of why and how.

[Cliff R]

+2 and thanks for the science involved with this deal.

We get enough calls to the shop from folks using mechanical pumps and experiencing difficult hot restarts that I'm sure this new fuel trapped in the line between the pump and carb at shut down is causing issues with pressure rise.

Never once had a call from someone with an electric pump, or running any sort of return or bypass, it's ALWAYS using a mechanical pump and dead-head to the carb.....something to ponder on......Cliff

[mrtonegto]

Thank you very much RobbMc - the pros knows................

I will be blocking the return on the pump.

Tone

[mrtonegto]

What is the appropriate way to block of the VR on the pump?

The pump has never had fuel in it, so maybe some sort of solder???