livelotus

I recieved the suggested fuel pump for my GMPP ZZ383, it's a NAL-12355612. I does not have a fuel return. Do I just cap my return line and be happy or do I need to get a pump that incorporates the return line.

FYI: I'll be using my old quadrajet and I believe (think) I don't need a fuel regulator.

Any and all words of wisdom are welcome.....


Thanks

H

...Roger...

I like using the return.

lars

The formulation of modern fuels is conducive to severe boiling in the carb bowls and vapor locking of the sucking side of the fuel system. Due to drivability problems at low rpm on hot days (like when "cruising"), I haven't built any engines in recent years without a return line. You have nothing to lose and everything to gain by running a return. You might get lucky and get away with a non-return system - if you happen to have good fuel in your area and your carb system is not prone to boiling the fuel in the bowl(s) you'll be okay. But if I were you, I'd run a bleed oriface near the carb inlet and run a return line back from there just to keep cool fuel circulating past the carb at all times - this will allow you to keep your current pump. This will give you a very reliable fuel delivery system without the possibility of vapor lock and boiling issues (provided you also install a reflective carb shield).

Lars

...Roger...

Lars the return pumps use around .070 orifice is this the size you use ?
Also is anyone using the old 69 fuel filter with the built in return up close to the carb for the return and do you know what the orifice size is in this filter ?

lars

Roger -
On the systems I've been building that do not use a return-style regulator, I've been installing a "T" at the carb inlet with an .060" diameter bleed hole in it and running a return line back from there - this seems to circulate a nice amount of fuel without affecting fuel pressure or volume to the carb. My personal preference is to use a Mallory return-style regulator at the carb, use a slightly over-capacity fuel pump, and let the reg do the work, but this results in a very non-stock fuel system, and it's a lot of plumbing work for most people.
Lars

...Roger...

Thanks Lars

livelotus

Thanks Roger and Lars,

I will get the return type fuel pump. Though I believe your regulator return idea is brilliant. I will consider the regulator if Ido have fuel boil issues.

Howard

FKING1

I've been running my 70 with a ZZ4 for 2 years with the return line plugged since had same prob with the fuel pump.
As long as the pump is not putting out over 7psi there is no need for return. If more, put in a regulator.

lars

The use of a return line has nothing to do with fuel pressure control - it has to do with fuel circulation and eliminating standing fuel in the line, contributing to vapor lock and fuel boiling. We run return lines on all engines, whether running electric or mechanical pumps, and with fuel pressures as low as 4 psi from the stock mechanical pumps. The return lines positively eliminate hot-weather fuel supply problems. When electric pumps are used at the tank, return lines are essential to prevent dead-heading the electric pump, lowering amp draw, and keeping the pump cool for maximum service life. There is no good technical reason to cap off a perfectly good return line system. Why do you think GM spent the money to design and install them...?

Lars

Mike Ward

So people could second guess and then undo perfectly good stuff they don't understand?

...Roger...

Not speaking for Lars but I think he is noting that the T in the line close to the carb is better than the return type pump.

lars

GM's return line from the mechanical pump solved the actual "vapor lock" problem: Vapor lock occurs on the suction side of the pump, and is a result of heat and low pressure on the suction side causing the fuel to vaporize in the line on the suction side of the pump. As soon as a diaphragm-type pump takes a "gulp" of vapor instead of liquid, its presure drops to -0- and you get the classic "vapor lock" symptoms. But this does not solve the problem of fuel boiling in or near the carb. By running the return line from a point near the carb inlet, you solve the problem that GM fixed with the pump return, and you also allow cool fuel to circulate near the carb to solve the secondary problem. Additionally, it allows the use of aftermarket non-return pumps.

Lars

lars

Yeah, you got that one right...
Lars

ssenay72

Any fuel pump recommendations? (with the return) And where do you recommend buying one?

...Roger...

The AC pumps are the only ones I've found that consistently have good check valves to stop return flow to the tank.

gingerbreadman1977

i have not had any problems with no fuel return lines . im not saying you wont from what everyone has been saying but im just throwing out there that on 2 different cars..one a holley pump and the other the stock gm no problem so far 5 and 2 years later

ssenay72

I tried three different aftermarket pumps and everyone of them leaked at the fittings. Put a stock one on and its been fine so far.

lars

You're in Australia. The gasoline you have there is completely different from the formulations we have here in the States. Our vapor pressure is much higher than yours. You're still running the gasoline that we had here in the 60's and that these cars were designed for. That's not the case here in the U.S. any longer.

gingerbreadman1977

isnt that a climate thing. there is generally warm temperatures here so fuel components of higher molecular weight and lower volatility are used. our summer to winter change is generally pretty mild so voletility doesnt need to be adjusted all that much between states and stations.

if it became a drama i guess an electric pump might be an option as well.

lars

Here in the States it's a political thing with nothing to do with climate. Each State has different fuel formulation and volatility requirements, with varying amounts of oxygenated products added to the fuels based on State mandated requirements. In some States, enthusiasts seem to have few, if any, problems with fuel supply and vapor lock issues. Other States cause severe problems for enthusiasts running carbureted cars with suction-type fuel pumps and no return systems. Henry Olsen from Ole's Carbs has written an informative article giving an overview of the subject - you can e-mail me for a copy of his write-up. This article gives a general factual overview of the fuel situation, but the solution to the problem becomes up to the individual enthusiast depending on what part of the U.S. you're in - I build cars that will run reliably in any State, and this requires the use of return systems. Chances are good that in Australia you do not have the Maize-Growers' Association mandating 15% maize-produced alcohol added to your gasoline... try running that crap on a hot summer day in a carbureted engine with stagnant fuel in the lines and bowls...

Lars
V8FastCars@msn.com