[Dick Boneske]

There are many large 2G carbs that function well as a substitute for the correct 7031575 float bowl and 7031587 airhorn.

Differences on most of these clones include:
*Usually no idle vent
*Added air channels under the venturi cluster. ('68 and newer)
*Added brass tube adjacent to the power valve rod (about '69 and newer)
*The use of phenolic floats vs. brass (all after '67). .
*Differences in the throttle body with choke, vacuum nipples, and provision for ported vacuum

.I have used clone center carbs for '66 Tri-Powers. Some owners want larger venturi openings vs. the correct '66 that has 1.180". I have used clones that are as large as 1.315" for slightly more cfm

I have not found an explanation for the added air channels under the venturi cluster, nor the purpose of the added brass tube next to the power valve rod.

The differences in the throttle bodies is normally not an issue--sometimes a bonus if the customer needs an additional vacuum source.

I would appreciate it if someone more knowledgeable than I would explain the added air channels and the single added brass tube.

[Goatracer1]

Ames used to sell a "cloned" center carb for the 1966 TP. I guess the reason they don't sell it anymore is shortage of cores. I have had one on my 1966 TP for several decades with good results.

[Kenth]

Dick, the added air channels is a part of the adjustable off-idle air bleed system.
An adjustment screw is located at the end of the channel to control the amount of air bleeding into the system.
The off-idle screw is adjusted at the factory to maintain very accurate off-idle air/fuel mixture ratios.
It is adjusted during carburetor flow test, then capped, and no attempt should be made to readjust in the field.

The single brass tube is a part of the fuel POE system adding fuel at hard acceleration and high speed driving to compensate the somewhat lean main jetting for economy. At approximately 8 pounds of air flow per minute and above, the fuel begins to feed from two discharge holes located in the air horn just above the choke valve.

HTH

[carbking]

There is a bit more to this story.

There is a large number of 1966 Pontiac tripowers that have the wrong center carb. I wondered about this for some time until a "gentleman" with a magnolia blossom accent called wanted to buy all of the 1966 center carbs I had. I wouldn't sell them separately, and I asked his why he wanted them. He told me the 1966 center carb was the largest Rochester 2 barrel (it isn't), and flowed the most CFM (it doesn't); and he modified them for the southern dirt circle track racers. He told me at the time, he had personally modified more than 50, but he needed more. So once again, fiction can be more important than fact.

Goatracer1 mentioned Ames. Steve and I were good friends, and Steve asked me to come up with a possible clone. I don't remember the exact number, but one from about a 1969 or 1970 Firebird was perfect if one used mechanical linkage. Steve started acquiring and selling these as clones.

Jon