I just got a Carter fuel pump (mechanical), and it only has a inlet and outlet connection. The stock pump I had on before had 3 connections....inlet, outlet,....and another one that comes from the gas tank. What's that one for??

It's a 83 Z28 305 carb.....

 

The extra smaller hose is a return line. It sends the excess fuel back to the tank. All you need to do though is plug up the return line with something like a bolt and put a clamp on it to keep the fuel from coming out of it.

 

The return is there because of vapor lock. Instead of just dead-heading when pressure is reached, the return sends the excess fuel back to the tank. This has the effect of not keeping fuel around hot engine parts.

If you are going to drive this in stop & go in hot weather, I'd suggest you take the Carter back and get an AC replacement. It will more than likely handle your fuel needs, and in the unlikely event that it doesn't, put an electric pusher back by the tank to assist the mechanical.

 

Thanks 5-7.....I thought it was either some type of tank vent or a return line...

I think I may have the "unlikely event" you refer to. Sorry I didn't elaborate that this is for my 400, not the 305. The engine builder says a high volume pump is required, which is why I got a high volume Carter pump. They claim it puts out 120 GPH vs. 60 GPH from a stock AC. I don't want to run an electric pump if I can help it due to reliability issues.

Learn something new every day -I always thought only electric pumps required a return line, not a mechanical.

Now that I know it's a return line, can I connect it to the opposite end of the duel inlet at my Demon carb on the fuel log? Or will this greatly reduce the volume?

And yes, the car will be mainly street driven. TIA for any help.

Also - if there's someone else that's converted over from a Q-Jet to a Speed Demon, I'd love to know what you did about the vacuum lines from the brake booster and carbon canister!!

 

Five7Kid is right abouyt the vapor lock. Thats why I recently had to go back to the stock unit from my Holley pump. The preasure would not hold when the engine got hot.

There are aftermarket mechanical pumps with returns on them if it's the volume you need.

 

Thanks, and it makes sense. But what about using the "return line" connection on the opposite end of the dual feed inlet manifold that feeds the carb? Is that what it's there for? I can buy a -8AN to 1/4 inch hose fitting and just return fuel that way right?? So long as I'm returning a little fuel back to the tank, no vapor lock right?

 

OK, searched again and found this post. I assume I don't really need to return fuel then??

https://www.thirdgen.org/techbb2/sho...lume+fuel+pump

 

A 3-port reg w/return is the proper way to do it. If you just hook the return line to the carb fuel line, it'll have next to zero pressure - just the restriction the return line offers, which isn't much.

I've seen guy use a needle valve on the return, but that has to be adjusted under max demand conditions.

If vapor lock is a concern, use a reg w/return. An electric back by the tank with the reg is the surest way to go.

BTW, a replacement AC pump with return will more than likely be adequate to feed your 400 (I knew that's what you were building when I originally responded).

 

Well, it seems I need to do one of three things then.

1. Return the pump, and put the stock one in. Then I'll have to figure out how to adapt -6 AN steel braided hose and fittings I already bought to the outlet of it.

2. Keep the Carter pump, plug the return hose and hope that vapor lock won't be an issue.

3. Find a three port regulator to install after the pump and return fuel that way.

I guess the big issue that will determine which I need to do is vapor lock. So, are others running no return hoses and not having problems with vapor lock??

 

Shoot a note to RB. He's talked often of running a 400 on a stock pump in a daily driver.

 

Nah, that's OK 5-7... I believe you. I decided to just return the thing. I got it from Summit and the pump was in a regular cardboard box that had a "Resealed" sticker on it. But - it also said ALL the parts were verified to be there by Summit professionals - (yeah,right).

Of course it was in fact, missing the fittings/adapters the instruction said were "provided". So I'll bolt my stock pump back on and see how it runs.

Thanks!

 

Maybe five7kid has had more luck with the AC pumps than I have. My replacement pump did nothing. Did not solve the starvation issues at high RPM, did not solve the off idle stumble caused by vapor lock, did not solve the stalling at extended idle in 95* weather.

I put in one of Carter's street mechanical pumps along with Carter's electric pump by the tank (per Damon's recommendation). Both internally regulated to 6 psi. I just removed the return line and capped it at the tank. Solved all my problems, and it maintains a constant 5.5-6psi at all times. No vapor lock.

 

"If I were a rich man", I'd have an electric back by or in the tank, and a 3-port reg with return.

But I ain't, so I don't.

 

So it is a small world. Ill just add that I think using the 7 PSI oil pressure switch off the 2.8 would be a good idea for anyone with an electric pump. Now its not set up as a safety switch on th 3rd gen but can be used as one so its only pumps when you got oil pressure.

You could get burnt up in a crash if the pump kept going.
Though in my 2.8 Bird it is set up that way. Only the oil switch turns on the pump. So it must turn over a time or two till it hits 7psi oil.

 

I was / am maybe gonna do just that. Elec pump in the rear [ its a 12-16 psi pump] run it to feed the Mech pump, which has its own bypass and return [ 3 hose pump] on a 7 psi oil switch.

wouldn't the / isn't part of the return on the 3 hose pump a regulator in its self??? or maybe I wonder what or how they are set. Say the floats blow open at 10 psi so the return on the 3 hose pump should by pass at what 7-8psi?

I wonder how or why it bypasses at what settings. It may just be a factory set 6-7 psi regulator built in. Making an extra one useless as it wont let any more than that by.

 

The pump return is a relief valve, acting very much like the valve in the oil pump. So, yes, it is acting as a regulator, and I have proposed in the past that you could use a pusher electric at the tank and let the 3-port mechanical act as the reg in the front. You could even leave out the push rod if you like, the pusher would apply the pressure at the carb. I was flamed pretty lustily for this suggestion.

 

Thats what I thought. pop out the pin or cut the level on the Mech pump, but still run the Elec pump [gas] through it so it acts as a regulator and return excess fuel. Makes sense to me. Get an extra 1/4 HP too.