Engine Hesitation Help

I have a 1979 200 3.3 V6 Chevy w/ mechanical fuel pump and 2bbl Rochester carburetor. The engine is factory stock. The engine starts and runs fine. In park or neutral it revs fine w/ no hesitations.
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Problem<O</O
The engine accelerates fine but when the car reaches 30-40 mile per hour, it starts to hesitate, spit and sputter. It seems as if it is starving for fuel. The engine never dies or stalls.
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My first thought is that the carb needs to be cleaned or rebuilt. Maybe the floats are bad or sticking. But like I mentioned it always starts and revs fine w/ no hesitation.
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I replaced the plugs, wires, distributor cap, rotor and coil. Thou these items needed to be replaced, it had no effect on the hesitation problem.<O</O
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Is it possible that the mechanical fuel pump is not delivering enough fuel when the car reaches higher speeds? Does a mechanical fuel pump go bad?

<O</OAm I approaching this the wrong way? Could it be something entirely different rather than a fuel problem?
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Please help me out guys. Your thoughts and opinions are greatly appreciated.
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Thanks,<O</O
Matt

 

check your fuel filter, also I know 4 barrel q-jets have a filter in the carby at the inlet pipe, if yours has one take it out and leave it out.

 

The crab is a 2bbl rochester. The fuel filters look to be ok.

Do you think it could be the accelerator pump?

 

bump

 

Doubtful if it is accelerator pump. Sounds more like starvation problem. Can you get it past 30-40 mph or not posssible? If so, what does it do on a steady cruise at say 50, then you accelerate? Does it hesitate instantly or does it take a little bit before it starts to stumble? What about from a dead stop, does it hesitate at all or no? If it will accelerate from a dead stop without hesitation, then probably not accelerator pump.

 

Not possible to get it past 30-40. When I accelerate, it hesitates instantly. If i punch the gas hard from a dead stop, it does hesitate.

Could it be the mechanical fuel pump?

I also noticed that some of the steel fuel lines have been replaced w/ rubber gas lines. The line in question is the one from the fuel pump to the carb. Could teh rubber lines cavitate during fuel delivery?

 

What does this have for a dist?

 

Factory distributor.

 

Does it have a vacuum advance?

 

My guess would be a distributor problem .Is it an Hei .Ok I went back and read .If accelerator pump on carb is ok ,Trya rebuilt distributor .My pontiac distributor was so worn out It lost power around 40 miles an hour ,It was fine up to that speed .I didn't punch it though .If carb checks out first .Filters and so on .

 

Check carb to see if base plate screws are loose .That was a common problem with 2gc .I just remembered .

 

my money its an ignition problem if it runs fine in park but runs like **** with a load on it try have'n some one hold the break while holding the noise lever down to about 1800-2000 rpm and spray water out of a squart bottle on to the plug wires and you will find your (ignition break down)

 

Matt, you did not say if said engine has been transplanted into something else, or is still running in original form through a stock exhaust. If it has a catalytic converter it might be plugged, drop the pipes at the header and take it for a drive. If it has already been modded disregard.

 

The distributor does have a vacuum advace. How do I tell if it is an HEI?

 

pickup coil?

 

If it has bronze factory fuel filter take it out.Hard to tell if bad by looking at it. Rubber lines may be ****ing air ,Or collapsing from suction, If in line from tank to pump. Hei dis has no points. Muffler/ Exaust pipe may be collapsed . Factory exaust on some gm cars in those years had double wall exaust tube betwen manifolds and cats/muffler.These would collapse the inner wall,the outter wall looks fine.but no exaust can get thru.

 

Fuel starvation problems act kind of wierd, the carb has a float bowl, which usually gets filled just fine when the engine is idling. Then as you drive the car, and use fuel, it will lower the level as fuel is drained out but not refilled fast enough. When the level gets down too low it will lean out and sputter and cough and not accelerate at all.

But if this is what's wrong, it usually takes a bit of time for the fuel starvation problem to take effect. So it will accelerate OK at first, then get worse. If you cruise at a steady speed like 25 mph, then mash the pedal, it would go ok for a bit then start coughing or bucking.

If it's an ignition problem, then it probably will act up the same under the same conditions all the time. There won't be the time delay that you see with fuel starvation.

HEI on those had a coil in the distributor cap.

If you pull the cap off you might be able to see a problem with the mechanical advance, which is just under the rotor. It might be stuck, or the pins might be worn so it moves too far, or does not advance as rpm increases. If it looks bad, get a rebuilt distributor. You should be able to turn the rotor clockwise a little ways, against spring pressure.