Engine wont start, what now

hey i have a 68 firebird with a late 80's early 90's motor. The engine simply seems to have a problem whenever I start it up. The needle tach will jump all over the place and the motor will also sputter and do the same. It dies if i take my foot off the pedal. Now i changed the rotor, cap, spark plugs, and had the carb rebuilt. idk what their is next i can do! Odd thing though is even while its sputtering i quickly take it out of the driveway, put it in drive and hit the gas, while i am driving down the road the RPM tach and the engine will jump and sputter less and less, then after a few minutes of driving it goes away. The past few weeks though it has gotten WORSE. Now it will start for a few seconds without the RPM needle jumping(bascially running normal), then after 10 seconds it jumps and the symptoms start, then it dies. At this point, the engine wont start even after i put starter fluid in the carb. I wait about an hour and then it starts right up(sometimes). Idk what to do next. Distributor? maybe vacuum leak? Carb could just be shot? What doesnt make sense is that this is intermittent. I drove it fine all day yesterday after it did these symptoms early in the morning. Here are links of the video of my car to show you what i am talking about.

http://www.youtube.com/watch?v=2z7Ipy81Up4

Check all of your grounds (and make sure you have enough of them). Sounds like a bad contact somewhere and once things warm up and expand the contact gets better. Putting the car in gear may be moving the motor mounts etc. enough to create an easier path for the electricity to the battery than the block to battery cable.

Has it got trash in the fuel tank ?
Like old rust , crud , etc ...
You could be pumping trash through your rebuilt carb ..
Also , put a vacuum gauge on the intake and see what you get ...
You may have a bad fuel pump ..
You may have some wiped-out cam lobes ..
Pull a valve cover and see what the rocker arms are doing when you turn the engine over by hand ...
Pull the spark plugs out . It makes it easier to turn the engine over by hand ...

I can think of a few possibilities but really need to know some specifics on your engine combo. First off, is it a HEI or points distributor? What type of coil? Q-jet, Holley, or Carter carb? Aluminum or cast iron intake? Some of the first items I would check is your plug wires (resistance) and if it's a points type dist, check the dwell. (point gap)

Your tach or Distributor power wires may be shorting out. The erratic tach needle seems to indicate some kind of short. It might be something inside the distributor, but you haven't told us what you have.

MSD ignition?

I agree, try disconnecting the green wire at the coil and driving it again.

But the way it acts on the highway it might be an idle circuit issue. Plugged or restricted.

Its a HEI distributor, edlebrock, aluminum intake, and my next step is buying a pressure gauge for the fuel pump, the filter is clear so i figure id know if the fuel is bad??? Maybe idk. Yesterday after driving it all day all the sudden its now doing something a little different-the symtoms it does when it starts up, is NOW doing it when i drive after its already been running for quite some time, this was when i was heading home. Would you guys all think it could be something different now since its doing it even after its been running sometime?

I've seen bad plug wires do strange things on an HEI distributor. It can cause voltage to arc down inside the cap to the module. The module grounds through one of the hold down screws, I had one that was stripped that caused intermittent problems. The pickup coil can go bad in addition to the module.

Could be a bad Module in the HEI. I know for most people that the modules die when they are hot and leave you sitting until the module cools down and then the car runs fine. The module can also have issues only when cold and run fine when warmed up. Change the module, they are cheap. If the problem persists the next place to look would be right where Daivd said, the pole piece and pick-up.

When the engine does not start (even with starting fluid) are you checking for spark with a timing light? I don't think this tach issue is a coincidence. Like 406 Q-ship said, Your symptoms are that of a glitchy module. I would check for a consistent spark at idle with a timing light to verify whether its the tach signal or actual spark to the engine that is misfiring.

The boys are correct to say the ignition module. They are exposed to a ton of heat and go bad all the time. The thing that bothers me about that is they usually fail when the engine gets hot and are fine when cold. This is the opposite of your problem but stranger things have happened, and since it is cheap and easy it is definately worth a shot. Whatever it is it sounds like an electrical rather then a fuel problem so I would look there first. Plug wires may be shorting to one another check those and replace if they are suspect. After that check you ground connections. A very common mistake is that people assume that a screw or bolt though a painted surface will be a good ground. This is not true. You need a nice clean surface to provide a nice clean ground. Good luck with the hunting.