Reply to "carburetion"

Holley 4150 carbs are decent once they're dialed in for a motor. The trick is setting-up the ignition properly and then setting-up the carburetor properly.

Holley's double pumpers are set-up rich out of the box in the idle circuits because they're set-up for a motor with a high overlap cam and therefore lower than stock idle vacuum. Mount a carburetor jetted that way on a motor that has a mild cam (high intake manifold vacuum) and it draws too much fuel at idle. Of course the carb can also be set-up wrong, i.e. the primary or secondary butterflies may be open or closed too far exposing too much or too little of the transfer slots, or the idle jets are improperly adjusted. And then there's the setting of the fuel bowl floats and the vacuum rating of the power valves.

How have you set-up the motor's ignition timing? Is the motor equipped with a single plane or a dual plane intake manifold? What's the intake manifold vacuum at idle? Have you replaced the cam ... if so what's the new cam's specs? Was the carb new or used? If used did the previous owner modify it? Does the carb have copper or black phenolic floats? Phenolic floats will float less and less with age. What's the list number of the carburetor? If the carb is new are you using it jetted as it came out of the box?

There are Holley 4150 style carbs that are jetted properly for a street engine out of the box (Quick Fuel Technology). And there are shops who specialize in tuning carburetors for specific engines. There's several ways to resolve the issue.

-G