Twin 600's are too much for a 350CID, or 383 for that matter. You are most likely over carb'ed, and running too much air/fuel for the street. Switch to twin 500's to cut down on the volume of air and rejet to 107's, with 73-42(part #1455) metering rods with 8"(silver) step-up springs. This combo gets a full boost of 20 earlier with a 1.1 blower drive.
Last edited by carsavvycook; 04-24-2008 at 05:26 PM.
Reason: additional wording