lars

Don -
I think I posted answers and photos to all your questions in my posts above, including photos of a QuickFuel carb with return, and a regulator-type return system. These systems are exactly what you're asking about...

The non-return fuel pump with your setup is a huge problem when it comes to vapor lock. I install fuel return systems on every car & engine I build now due to this problem, and it's essential to have a good return system if you intend to run a carbureted car on today's pump gas in warm climates.

The QuickFuel carb makes a return system very easy to install as shown in my photos above. The first photo of the QuickFuel is the basic bleed-orifice system as Rob is running. It uses a small drilled orifice in a restrictor fitting at the rear carb inlet "T". This works just like the GM return-fuel filters with the 3 connections (simple bleed orifice for return fuel) that GM used with Holley carb systems in the 60's. Fuel bleeds through the restrictor and keeps cool fuel circulating past both carb inlets.


The better system, but a little more complicated, is to use a return-style regulator as shown in the photo of the engine with the Demon carb. The regulator is simply set to a pressure slightly below the pump oulet pressure, and it continuously bleeds fuel back to the tank to eliminate any vapor lock issues. Since your car has the return line installed down on the frame, it's an easy tie-in to create the return system.


Lars

BlackC3vette

Lars,
Are the return lines that you have in the pictures 5/16"?

If you are recommending a separate return line all the way back to the top of the tank, is there an accessible fitting on the tank? Does the tank need to be dropped and a fitting installed (welded/drilled)?
Or, can you tee into the 5/16 rubber hose return line (Edelbrock mechanical pump)?

donyue

Hi Lars, thanks very much for your reply. Your help and knowledge is greatly appreciated.

I'm off to go and purchase my Aeromotive fuel pressure regulator with the return port and associated hoses to connect it to the Edelbrock fuel pump and stock fuel return line on the frame. I suspect the addition of the fuel return will solve the vapor lock issue and the Aeromotive fuel pressure regulator will allow me to add a greater capacity electric or mechanical fuel pump in the future should I decide to add power adders or revise the engine to run EFI.

Thanks Don

AzMotorhead

Lars are the return hard lines pictured Stainless steel or aluminum?
If SS what tube bender did you use to bend them?
Nice marker you used on the fuel line BTW

lars

I have 2 different systems shown in the photos on the previous page of this thread. The first system is a simple bleed-orifice system, of the type used by GM. It uses a .060" diameter hole in the restrictor fitting shown so that a little fuel will continuously bleed back to the tank to prevent vapor lock on the suction side of the fuel pump. Since very little fuel is bled off down the return line, the system shown has a 1/4" stainless hard line that runs down to the stock 5/16" line on the frame rail. If the car is equipped with a factory 5/16 return line (all C3s were so equipped), there is no need to add any additional return line - just use the factory line and tie into it with a rubber splice section. The return line is not under pressure, so you can safely use rubber splice sections for connections to the factory steel line. If the car does not have a return line, like my '64, you have to run a line back to the tank and drill the tank for a bulkhead fitting.

The second system design shown uses a return-style regulator. In order for the regulator to work effectively, you have to run a return line no smaller than 5/16. AN fittings and hardware normally do not come in 5/16 ("AN5" size), so I used 3/8 lines for the return system on those setups. The return style regulator runs a significant volume back to the tank, with the intent to keep cool fuel at the carb inlet at all times. This system is very effective in eliminating any fuel supply issues caused by hot weather and pump gas in a street-driven car. This type of system is also very effective for use with electric fuel pumps: Electric pumps don't like to be "dead-headed." By allowing fuel to continuously flow through the pump, the pump amperage is lowered, the pump runs cooler, and pump life is extended significantly.


All the lines shown in my photos are stainless. I don't like using aluminum lines, so for my nice "custom" builds I use stainless, and I use stock-type mild steel for the "restoration" projects that need double-flared inverted flare fittings (you can't double-flare stainless). I use a Bluepoint tube bender as shown in my article "How to Build a Fuel Line," available from me via e-mail request. This is the same bender sold by Snap-On.

Lars

BlackC3vette

Excellent explanation!

AirborneSilva

Sorry to ask a question that may be obvious to others but should I make a return line from my carb and T it into the return line from my stock fuel pump? Thanks and sorry if it's a no brainier type question

lars

No, that won't work. If you're going to make a return line from the carb, you need to remove the return line from the pump and cap off the pump return nipple. You then run the return line from the carb down to the return line on the frame rail that the pump was hooked up to.

If you run a return line from the carb and T it into the return line coming out of the pump, you've simply created a loop that will flow nothing. Run one or the other systems, but don't T them together and try to run returns from both the pump and the carb.

Lars

BlackC3vette

Using the hose that was connected to fuel pump return line was easy to understand (assuming I understood correctly). The question I now have is in regard to the mechanical pumps return fitting. Capping off that fitting won't create any internal pressure problems in the pump?

AirborneSilva

Thank you Lars, that makes perfect sense

lars

The return nipple coming out of the pump is just a simple fixed-orifice bleed off the pressure side, which allows a slight bleed of fuel back to the tank to keep the fuel on the suction side of the pump circulating, thus preventing vapor lock on the suction side of the pump (which is where vapor lock occurs). The pump is a diaphragm-type pump, which is not a positive-displacement pump, so it can be run dead-headed with no adverse effect: it is internally regulated to limit output to less than 7psi. By moving the bleed return from the pump to the carb inlet, the pump "sees" the same effect, but you get the benefit of circulating cooler fuel close to the carb inlet, which reduces the tendency of fuel boiling in the carb bowls and accel pump wells.

Lars

frankinvett84

Sorry to revive "old" thread...But... The regulator in the photo of Lars engine (corvette valve covers) looks like its after the carb so is the fuel going into the carb unregulated?
I would appreciate any ones input. Thanks

terrys6t8roadster

This is what I came up with for fuel return. The tee no 6 AN fitting drilled out to 5/16 fine thread, a 5/16 set screw drilled out at .073, then screwed into the tee. Then reduced to no.4 AN 1/4 in. with push lock fitting, 1/4 hose to OEM return line. T

lars

Yes, the reg is located after the carb. It's a return-style reg, so you can run it either before or after the carb, depending on how you plumb it. When it's used after the carb, the regulator constantly bleeds enough fuel out the back end to keep the supply pressure constant at the desired setting at the supply inlet. It works exceptionally well, because it continuously circulates cool fuel right past the carb inlets, effectively eliminating any possibility of vapor lock:



You can also install a return regulator in front of the carb. When you do it this way, the regulator inlet sees pump pressure, and it blows fuel back to the tank to keep the outlet at the desired setting. Here is a before-carb application of the same regulator - it's just plumbed differently to allow the different circuit flow. This setup does not keep the cool fuel circulating as close to the carb inlets as the after-carb setup above. The choice to locate it prior to the carb was simply a matter of available "real estate" on this supercharged engine:



Note that on the pre-carb setup, there are 3 lines hooked up to the regulator in order to make the return system work. On the after-carb setup, you only need 2 lines hooked up.






Lars

lars

That's a nice, simple, effective system that will work perfectly. And it's all tucked out of sight once the engine is installed. Nice work!

Lars

PAmotorman

remember any fuel return system that is in the engine compartment will pick up heat and you are returning heated fuel to the tank and after a while you will raise the temp of the fuel in the tank, not good for a performance car

lars

Every modern fuel injected performance car built has a fuel return system from the engine compartment... but maybe your C6 is not a performance car...(?)

John McGraw

Nope, GM did away with the engine return line many years ago on their performance cars. I believe that 98 was the last year for a return from the engine compartment on F body cars, and Corvettes have never had one since going to the LS engine. They use a rear-mounted combination filter/regulator, with a short return line to the tank.

I don't know what they are doing on the new, direct-injected LT engines.


Regards, John McGraw

PAmotorman

thanks as i was going to post this

lars

The injected cars I have in my garage all have the pressure regulator, and the return line origin, on the engine in the engine compartment, but perhaps the injection comparison was a bad choice, and irrelevant to the conversation in this thread: Injected cars with the pump in the tank don't need to run a return to avoid vapor lock and carb bowl fuel boiling, since the fuel supply line is pressurized to about 45 psi all the way to the injectors - the only purpose of the return is to regulate the pressure, and to prevent the fuel pump from dead-heading, so the return can be placed at any location. You are correct.

That's not the case on a carbureted engine with an engine-driven fuel pump. To avoid vapor lock, the fuel return must come all the way from the fuel pump, which is located in the engine compartment. And to avoid heat saturation of the fuel in the line between the pump and the carb, and to reduce in-carb fuel boiling, the return is always placed as close to the carb as possible on any high performance carbureted application. Take a look at the plumbing system in a NASCAR running in one of the carburetor-mandated classes and any competitive road race car running a carb. On our drag cars, we all run the fuel return over and through the carb float bowls and back to the tank. It's common practice on any high performance application.

Are you suggesting that a fuel return line not be used..? I'd like to see that done on a street-driven car with a carb in hot weather running up a long hill... If you've had luck with that, you're much luckier than me... I install full-length return lines from the engine compartment on every car I build. If I could avoid the time and expense of doing that, I certainly would.

Lars