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Author Topic:   Rochester Carb Size
Dirt Full Roller

Total posts: 34
posted May 03, 2005 11:46 AM  
Can anyone tell me the largest bore size that came stock and what they might be found in. This is in reference to the 2jet carb.

Also what the bore size might be on a 2bbl roch that came off of a 1974 350 Chev?

Thank You in advance

Dirt Forum Champ
Total posts: 1019
posted May 03, 2005 12:11 PM  
1 3/8" venturi is the largest, with a 1.687" baseplate (1 11/16").
Your 1974 carb won't be the "big bore", it'll have either a 1 1/4" or 1 5/16" venturi, depending upon the actual vehicle application.
You will find the "big bore" carb on early gas powered GM school buses (maybe), grain trucks, and the 1971 Pontiac 455 motor that came with a 2bbl option (although rare). They were on old trucks that had governors on the baseplates, and other such heavy duty applications. You'll almost never find one on a small block in a car or light duty truck from the '70's.

Usually, the last 3 digits of the number on the carb will be "118" for the big bore ones, but even that is not a sure thing, and there are many other numbers that also were a "big bore" body. For example, the Mercury 4cyl boat motor has a 2G carb on it that was sometimes numbered 17085107. That's a big bore carb with a special booster assy that has no cones in the boosters....

Good luck and let us know if you'd like help finding one.


[This message has been edited by KPLugnut (edited May 03, 2005).]

Dirt Full Roller

Total posts: 34
posted May 03, 2005 03:35 PM  
Thank You KP ...Your the man!!!

Dirt Roller

Total posts: 23
posted May 03, 2005 08:37 PM  
Yes KP you will find the large governored carb on school buses!!! Every one with a small block, bilt in the early 70's that I've found has one. And these have the coneless boster you speek of. The only problem is the main body has no idle speed stop. I weld a old push rod to the throttle body plate for the screw to hit.

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