Rochester Carb Differences?

Spag4203

Member
What is the difference between a Rochester 4MV 7041540 & 7041554?

I have a 71 GS 455 and bought a Rochester carb from O’Reillys and the card that I received is a 7041544. Are they all interchangeable?
 
While all Rochesters are not the same, those two rebuild to the same specs. They are interchangeable. You may want to keep the original carburetor in case you ever want to have it restored as "numbers correct".
 

LARRY70GS

Active Member
1971BuickQJet.jpg
First, I'm not sure where O'Reillys gets their carburetors, but if it is a Remanufacturer, I would never buy one. Any of the good rebuilders won't even touch a Remanufactured carburetor. What they do is put carburetors together from piles of parts, and they modify them for a generic tune. You are way better off just getting a junkyard Q-jet and sending it to someone who specializes in rebuilding/tuning them for your combination. Quadrajets were calibrated for the engine they were meant for. You can't just throw any Q-jet on an engine, especially one that is modified, and expect it to run right. A quadrajet meant for a 350 is different from one meant for a 455. A 455 needs more air at idle than a 350. The idle system/calibrations will be different. There are other differences. The 350 carburetor(7041544) will be a 750 CFM model. The 455 carburetor (7041540) will be an 800 CFM model. It has visibly bigger primary venturis, and is jetted richer. All big block Buick Q-jets will use the bigger castings from 1971 and up.
The title of this thread differs from what you say in your original message. The 7041540 is a big block carburetor. The 7041544 is a 350 carburetor The title says 7041554. Not sure if that is a valid number. In any case, the carburetor number may mean nothing if it came out of a Remanufacturer.

If in doubt whether you have a 750 or 800 CFM casting, look for the bump in the outer venturi wall. It is there to clear an internal passageway.
Q-Jet_venturi_differences.jpg
q-jet--800-bump-web.jpg
 
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