I have a 1964 Impala 409/340 hp with a 400 hp cam, 7000 rpm Isky lifters, and the original silhouette 4GC carburetor. I have installed the correct carburetor rebuild kit, checked the springs and re-curved the distributor. The fuel pump is a new Federal Mogul unit and I just had the jets in the carb drilled .005”.

The problem is the car does not run properly; as long as you accelerate it’s okay, but just driving at a steady speed it sputters along. I believe it’s starving for fuel, but I’m not sure what to do next. The drilling of the carb helped some. Any suggestions are appreciated.

Thanks

Marie Lankford

Kansas

First make sure there are no vacuum leaks. With the engine running, pay close attention to the carb base, intake hoses and fittings.

Next, it would be a good idea to “balance” the carb idle mixture screws. Turn each screw in until lightly seated, counting the number of turns. Average the number of turns and back the screws out that number (example: one screw bottoms at 4 turns, the other bottoms at 3 turns. Back both out 3-1/2 turns). After that, always turn both idle mixture screws together when adjusting.

Another possibility may be the distributor is over advancing. To check this, disconnect the vacuum advance line and plug it. Drive the car and look for any changes. If this helps, you might want to replace the vacuum advance unit (or leave the vacuum line off if it presents no other driving problems) or you may want to purchase an adjustable vacuum advance unit from your local speed shop. Crane and Mallory make these units.

Marty