i'm converting from tbi to carburetor and was wondering if I need to pull the fuel pump out of the tank or of I can just run a mechanical pump off the motor and suck fuel past the old pump in the tank? any help would be greatly appreciated. The thought of having to pull the tank makes me want to puke The pump in the tank is shot and won't run even if I bypass the fuel pump relay and wire it directly from the battery to the relay harness.

 

I am not 100% sure on this, but I do build mobile oilfield equipment for a living so I have some mechanical knowledge. Absolutely 100% you have to remove the in tank pump if you are NOT going to be using it. Your mechanical pump will be working so hard to try and pull fuel through it.

Have you thought about using the factory pump with a pressure regulator to get it down to the psi you need to run the carb? It could possibly be a return style regulator that relieves pressure back to tank? Just a thought.

 

Why the conversion? This can end up costing a lot of money. If I remember right most of the 305s after 1990 no longer had a CAM that had the lobe to support a mechanical fuel pump. I think the "Battle" between which is better EFI or Carb is long over and EFI won.

Trying to pull fuel through a broken fuel pump should not be considered an option.

The cheapest way to fix the fuel pump problem it to replace the fuel pump. Since you are not worried about keeping the car " all original" maybe you should just use the Hatch method. I have not done it on a 3rd gen but I have done it on a 4th gen. Search 3rd gen hatch method. If you are set on the conversion then with the stock setup you have to use a regulator with a return system. Your stock type fuel pump will overheat without it.

 

As suggested, change the pump in the tank - you'll be money and time ahead.
As Gorn suggested, no more lobe for mechanical pump.
One can pull fuel through the in-tank pump as it is a vane pump and produces 9-13 PSIG at the TBI test port.
I'm sure you jumpered in battery power to the correct terminal on the relay socket.
If you jumper to the fuel pump receptacle at the tank, does pump work?
Could be a corroded connection, both for power and ground.

 

I have done the conversion on a full size GMC truck and two S-10 trucks and I always just used a inline electric fuel pump with no problems. This take care of the problem of no fuel pump lobe on the cam. Just drop in a HEI and your set. If you ONLY have a bad fuel pump then JUST change the pump and keep the rest as is.

 

already running a aftermarket cam with fuel pump lobe on the cam. At the connector on the rear "bulk head" ??? where the wiring goes into the car. At that connection there are three wires. I would assume that one is hot one is to be grounded and one is fuel gage....does anyone know which one is which????

 

Tan wire would be for gauge.
Power would be ign/PCM controlled relay.
Black my be ground - check with ohmmeter to ground.
Haynes manual will tell you or a downloaded service manual.

 

Even though the block has the mounting boss for a mechanical pump, the block isn't open to the crankcase. You'd have to machine an opening to make it work.