A 4150 Holley carb is a square bore four-barrel with a primary metering block and also a secondary metering block. It's generally considered to be a high performance carb. One can change fuel metering by changing jets, among other things.
There are 4150s with mechanical secondaries and there are 4150s with vacuum secondaries. There are 4150s with one accelerator pump, and those nasty double-pumpers with two.
A 4150 is nearly always better because the other Holley square-bore still in production, the 4160, has a rear metering plate. While one can change or modify the metering plates, changing jets is just so much easier.
I like Holleys although there are plenty of other carbs and their admirers. Most any carb will run if it is tuned right, the last two words being all-important.
R.
