Sluggish Acceleration

• 1). Start the car and allow it to idle. Stand on the driver side of the vehicle and manually operate the throttle cable that simultaneously operates each carb unit, looking for any sticking or debris that may hinder the movement of the throttle body brackets. Spray the throttle bodies with carb cleaner spray and compressed air followed by a light grease. Test the cable again to ensure proper movement.
  
  
• 2). Turn the engine off.
  
  
• 3). Pull the throttle cable to a wide-open position, simulating full acceleration. During the movement, watch the accelerator nozzle within each carb barrel to ensure fuel is delivered to the bore throughout the acceleration, without delivering fuel before or after the throttle plates are done moving, which would flood or starve the engine; causing sluggish acceleration. If the nozzles over- or under-deliver, remove the nozzle screw with a Phillips screwdriver and pull the nozzles out with pliers.
  
  
• 4). Note the size of the nozzle by its numbered stamp. To increase the fuel delivery, insert a nozzle three sizes larger. Use a nozzle three sizes smaller to reduce fuel flow. Insert and tighten the nozzle screws and test the throttle cable again until the optimum fuel delivery is reached.
  
  

Rough Idle

• 1). Locate the metering block on each carb unit. Each carb will have one metering block, positioned between the fuel bowl and the main body where the throttle bores are located. On each side of the metering block, you'll find a screw. This is the idle mix screw, which will adjust the idle characteristics of each carb.
  
  
• 2). Turn both screws on each of the three metering blocks down until they reach their bottom. Back out each screw exactly 1.5 turns.
  
  
• 3). Start the engine and attach a vacuum gauge to the intake manifold's service vacuum port. Refer to your engine manual for the vacuum pressure range of the engine, a number you'll use to gauge when the idle mix screws have been properly adjusted.
  
  
• 4). Turn each screw of each metering block counterclockwise in half-turn increments until the proper pressure range is achieved.
  
  

Backfiring

• 1). Inspect the vents on each fuel bowl for debris or blockage. Spray with compressed air as necessary. A poorly vented fuel bowl will result in the buildup of fumes, causing a backfiring condition. Once this has been cleared, move to the jets within each metering block.
  
  
• 2). Remove the four corner screws from each fuel bowl with a box wrench. Pull each bowl off and preserve its gasket. With the bowls removed, the metering block main jets are now exposed. When the jet size is too small, the engine will be starved for fuel. This lack of fuel within the air/fuel mixture that enters the combustion chamber can cause backfiring, a condition that is damaging to the pistons, spark plugs and carburetor.
  
  
• 3). Unscrew each jet (two per metering block) with a screwdriver or pliers. Note the size of each jet (stamped on the jet head), and insert a larger jet size. Tighten each jet gently and press the fuel bowl gasket, followed by fuel bowl, back onto the metering block. Tighten all four bolts on the fuel bowl with a torque wrench to 7 to 8 foot-pounds. Start the engine and test the throttle cable, with all body parts away from the carburetor choke tower to ensure the carb jetting is correct. If backfiring persists, repeat this re-jetting process until the correct jet size is found.