You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re setting up a Holley carburetor for mid and high rpm power production.
Q: I have a small block Chevy 350, bored .030-inch over, in a 1970 Buick Skylark. It has TRW flat top pistons, stock 1.94-inch intake heads with Crane roller tip rocker arms, a COMP Cams 280-degree duration (advertised) cam, Edelbrock Performer RPM intake manifold, and a Holley 650 cfm double pumper carburetor. The ignition is stock HEI with a Moroso curve and vacuum advance kit and a Crane HI-6 ignition. Exhaust is Hooker headers with dual Flowmaster mufflers and an equalizer tube.
My question is, why don’t I have any power? My throttle response is good, but when I get on it, the engine falls flat on its face. It has no power anywhere in the mid to upper rpm ranges.
A: We suspect your power loss is due to carburetion problems. If you did nothing but bolt the Holley carburetor on, then you probably have some tuning to do. First, set the float levels and the air/fuel mixture screw. Check to make sure that your throttle cable or arm opens the throttle blades all the way; have someone sit in the car and push the gas pedal to the floor as you watch the blades open.
If the throttle blades are OK, then you need to work on the accelerator pump discharge nozzles, more commonly known as squirters. The pump cam (the plastic piece on the throttle linkage), controls the amount of fuel delivered, while the nozzle controls when the fuel is delivered. Larger nozzles quicken initial fuel delivery; smaller nozzles delay it.
Once you work out the bog with the accelerator pump circuit and have the fuel level set correctly (and providing the jetting is correct), you should have enough fuel to make the mid and high rpm power you’re now lacking.