86taproject

I have an 89 firebird that was originally a throttle body. I'm now changing it to straight carb(no computer at all). I'm using an LG4 engine though from an 86 trans am until i'm finished building my other engine. If i remember correctly the fuel pump on the carbed engine is mechanical and located on the side of the engine, but the car itself has the throttle body fuel pump in the gas tank. My question is what in the world should i do? I know that the one in the tank is gonna put out way too much pressure and flood the carb. Would i be ok to just use the fuel pump on the side of the motor and sorta bypass the one in that's in the gas tank itself? Or should i run a regulator like a mallory 4309 or what? I'm drawing a complete blank on what to do. I'm open for any suggestions at all.

RB83L69

Not too much of a twist, really....

Best thing to do, is use a block-off plate on the block; and the regulator you mentioned, set to 5psi or so. Mechanical fuel pumps don't do a real good job of sucking through an in-tank pump in many cases.

The main detail you'll need to work out, is wiring up the pump. You probably don't want to hack up your wiring any more than you have to, like this guy seems to want to do. https://www.thirdgen.org/techbb2/sho...hreadid=288346 Dykes and twisting wires together is a great way to have your car mysteriously die and refuse to work again when you hit a bump or something, or otherwise have mystery electrical intermittents. Ideally you'd want it to come on for a few seconds when you first turn the key on, and then to run only when the engine has oil pressure. Not too much of a challenge really, except for the intitial startup part. Even without that, it will work, as long as the carb has some gas left in it from the last time the engine was run.

86taproject

So removing the in tank pump and just running a simple piece of rubber hose at the bottom of the tank for the mechanical pump to suck through will not work?

RB83L69

Not a great idea IMO.

Although, if you wre going to go to all the trouble of dropping the tank to do that, the thing to do instead would be to get the "gauge sending unit" (which includes the fuel pickup assy) for a carbed application; use the mech FP; and not rig the car like that. i.e. just do it right. It's not that much money.

I wouldn't put rubber hose inside a gas tank no matter what. That's just not real bright. It swells over time with exposure to fuel, so it probably wouldn't last a year inside the tank like that. And, it would have no strainer, so any dirt or rust or whatever that's in the tank, will go straight to your carb. Basically you'd be installing some kind of a time bomb in your car, that gives you an iron-clad guarantee that you'll be back there re-visiting it someday.

86taproject

Thanks for the help RB83L69. The thing is i don't have to drop the tank at all. The guy before me cut the metal away from above the gas tank on the inside of the car so he could change out the fuel pump. So it's very easy to get to. So in this case, what do think i should do? You've been of great assistance. Sorry, i'm just a poor college kid trying to see what'll work. I want to do it the right way too, just don't want to spend an arm and a leg in the process.

RB83L69

Use the correct "sending unit" for a carb setup, and the block-mounted pump. Probably the best way to go.

vrtc350

iTrader: (1)

you could get one out of a junk yard from a carbed camaro. Be aware of the condition though.

86taproject

Thanks guys. You've been a huge help. You wouldn't happen to know what years or anything that would be compatible would you? Can i only get one from firebird or camaro or are there other body styles that used the same fuel sending unit? Thanks again.

vrtc350

iTrader: (1)

Here are a couple of articles that are helpful. This one gives an overview of the conversion.

https://www.thirdgen.org/newdesign/tech/carbswap.shtml

This article gives you the engine specs by year. Note the engine size and carb(you want the 4bbl) I doubt the displacement different will matter.

https://www.thirdgen.org/newdesign/tech/techdb.shtml

I am in the middle of this exact conversion. I'm almost finished building my 350. I just have to finish the light port job on my vortec heads. Here in a few weeks I will be pulling my wheezy boat anchor(305) out and setting everything up. I have the mechanical pump and I will give you any other part numbers of stuff I may get or need.

86taproject

I've got everything I need to do it, since it's a carbed engine already and i just ditched the computer controlled junk and installed all the noncomputer controlled stuff (carb, dizzy, coil). I'm just trying to figure out the fuel pump problem. Since i have the mechanical fuel pump, and seems like it is simpler that way, i think i'm gonna do that instead of use a regulator or deal w/ the tbi fuel pump. Thanks for the engine specs page though. That's what i needed to know. My only question is, will any LG4 equipped camaro/firebird use the same fuel sending unit? Or are there other motor sizes that i could use too? Thanks.

vejatabul

i simply wired the fuel pump to come on with a toggle switch and ran a holley $25 pressure regulator. just use the factory fuel pump relay and run a wire from the fuse box(key on power source) to the switch to the relay for the activation. i ran this on my vortec headed motor that ran 12.45 1/4 mile, with the exception of a 10 gauge wire to the pump, to the relay and on the ground.

vrtc350

iTrader: (1)

Now that is an interesting thought. What was the p/n of the pressure regulator you used. I'm not dead set on the mechanical pump. What about the return lines? Did you utilize all of the factory plumbing?

vejatabul

i just blocked off the return lines. the regulator was a holley 12-803. i just cut the factory lines and used rubber hose to the reg and then rubber to the carb(i later replaced these lines with an lines).

vrtc350

iTrader: (1)

So you ran a 10 guage wire from the pump relay to the pump for the ground?

vejatabul

no, 10 gauge for the power supply, and 10 gauge for the ground.

vrtc350

iTrader: (1)

gotchya!