1 This is the classic Holley 4150 carburetor, the user-friendliest, most tunable carburetor ever produced. This is a dual-feed 4150 with a secondary metering block, vacuum secondaries, and electric choke, which makes it a great street carburetor. The 4160 (not shown) does not have a secondary metering block and is more of a street carburetor. Also not shown is a 4150/4160 with mechanical secondaries, which is more for racing. Vacuum secondaries are more appropriate for the street.