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Old 04-26-2021, 10:12 PM   #2
Blue Bowtie
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Re: Carb suggestion for big block olds

A Rocheester 4MC/4MV is tough to beat. They have very good primary control - much better than Holley 4150s and usually better than a Carter AFB/ThermoQuad. The secondary can be adjusted fairly easily with metering rods, rod cam, and spring windup. A "plain/early" 4MC can flow 750 CFM without any modification. A "later" (after about 1971) 4MC can flow over 800 CFM.

They also require an intake which will accept the bore pattern. If you have a spread bore intake with equally sized bores, you may want to consider a Carter AFB instead, or change the intake. The Carter is a lot more configurable and stable than a Holley. Edelbrock offers new "clones" based upon the AFB design, but you will probably have a lot more adjustment involving all four jets and all the metering rods, in addition to the usual adjustments.

No carburetor out of the box is a "bolt-on" without adjustment. At a minimum the idle mixture will need to be set, and usually it is prudent to check the float level. It is very common to have to change at least the secondary jets (and metering rods) to tune for the specific engine.

It may also be reasonable to clean out and freshen up the current carb, if it is still viable.
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