Help!! Fuel starvation problem in 71 240Z!!

[trevorchiro]

Please help!! Appear to have a fuel starvation problem in 71 240Z.

Symptoms: Popping at higher RPMs. Popping with choke on. Popping during deceleration. Idles fairly well with no popping. When I try to accelerate from a dead stop the car sputters and wants to die. I have to push in clutch and rev up engine or put choke on in order to accelerate.

Done so far: Did full tune up and then went to adjust carbs. First adjusted air flow with uni-syn. Second tried to adjust fuel mixture. Front carb always seems to be too lean. Fully unscrewed mixture nut (away from bottom of carb which is supposed to richen mixture) and engine wants to die immediately upon pushing in pin on bottom of carb. Rear carb not as bad. With fuel mixture nut fully unscrewed when I push in pin it slightly slows RPM's immediately but not to the point of killing the engine.

From there I took apart and cleaned float bowls and Domes. Floats and jets seem to be in good condition. Pistons ride up and down smoothly in Dome and tapered pins don't appear to be bent at all. Also changed fuel filter.

Could I have a weak fuel pump that is not allowing for enough fuel pressure in the lines? What are the symptoms of a weak fuel pump? If so why is only the front carb affected? Any help would be greatly appreciated and please bear with me as I am a novice.

[xray]

Have you checked the float level? I noticed you said you cleaned it, but if the float rides too low in the chamber you won't have enough fuel available for higher vacuum conditions...

Re: fuel pressure... Tee in a fuel pressure gauge before each carb--should read 3-4 psi.

Raising the dome pin on one carb essentially "deactivates it" and is more an indication of the A/F mix of the OTHER carb. Raising the front carb piston causes engine to die means the rear carb is probably too lean.

[Bruce Palmer]

... A too low float would show up as fuel starvation (too little fuel in the float bowl) as well as a lean conditon from a fuel level too far down the nozzle. This could very easily be the cause of the pop. Let things idle for a bit, shut it off, and pull the dome and piston out of that carb and look down into the nozzle and SEE where the fuel level is in relation to the top of the nozzle. Ideally that level should be within a 1/16" of the top of the nozzle.

If you have to readjust your float, you'll more than likely have to readjust the mixture too, so be prepared to bring things to the proper settings in stages.....

[trevorchiro]

Have you checked the float level? I noticed you said you cleaned it, but if the float rides too low in the chamber you won't have enough fuel available for higher vacuum conditions...

Re: fuel pressure... Tee in a fuel pressure gauge before each carb--should read 3-4 psi.

Raising the dome pin on one carb essentially "deactivates it" and is more an indication of the A/F mix of the OTHER carb. Raising the front carb piston causes engine to die means the rear carb is probably too lean.

Thanks xray,

I will get to work on all of that and post the results later. Appreciate the help.

[trevorchiro]

... A too low float would show up as fuel starvation (too little fuel in the float bowl) as well as a lean conditon from a fuel level too far down the nozzle. This could very easily be the cause of the pop. Let things idle for a bit, shut it off, and pull the dome and piston out of that carb and look down into the nozzle and SEE where the fuel level is in relation to the top of the nozzle. Ideally that level should be within a 1/16" of the top of the nozzle.

If you have to readjust your float, you'll more than likely have to readjust the mixture too, so be prepared to bring things to the proper settings in stages.....

Thanks Bruce,

I will check that out and post results later.

[ktm]

"Symptoms: Popping at higher RPMs. Popping with choke on. Popping during deceleration. Idles fairly well with no popping. When I try to accelerate from a dead stop the car sputters and wants to die. I have to push in clutch and rev up engine or put choke on in order to accelerate. "

Popping from where? Intake or the exhaust?

[Nigel1943]

Check for air leaks around your intake manifold area both to the carbs and the head. Sounds like it's going lean.