Carburetor Blockage

• A blockage of dirt or burned fuel in one of the carburetor jets can cause rhythmic misfires as you open the throttle. An obstruction can prevent the correct quantity of fuel from passing through the carb and into the cylinder. If only one jet is affected, the cylinders will receive an uneven quantity of fuel, resulting in vibration. Because carburetors use different jets at different rev levels, the problem may be noticeable only as you accelerate.
  
  

Ignition Issues

• Ignition issues can result in the same problems as a blocked carburetor. If a spark plug is fouled or worn, it can prevent reliable ignition in one of the cylinders. If the other cylinders are OK, this will result in "rough" running when you step on the gas. A good solution is to replace all the plugs and see if this helps. When replacing the plugs, ensure you connect the distributor cap leads to the correct cylinders, because this determines the firing order of the plugs. Check your manual for the correct order; it varies among the different Firebird engines.
  
  

Drive Shaft Vibe

• The drive shaft connects the transmission to the rear wheels. It is responsible for transferring the power of the engine to the wheels, and so it is under a lot of stress. Some standard factory models are known to have their mountings slightly off-center, which can result in vibration at speed. You can try disconnecting the mountings and inverting the drive shaft, but this works only in a few select cases. The best fix is to replace the factory shaft with a high-quality after-market equivalent.
  
  

Gear Noise

• Factory-installed gears rarely produce noticeable noise or vibration, but after-market gear sets have been known to develop rattles and whines over time. Unfortunately, no known adjustments or modifications can be performed to combat this. The only reliable solution is replacing the gears with a new gear set.