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Old 03-08-2020, 09:58 AM
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Tom Vaught Tom Vaught is offline
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Quote:
Originally Posted by Kenth View Post
Thank´s for sharing you info Tom V!
In Delco Rochester Bulletin 9C-640 Date December, 1965 #7015106 throttle body gasket (vented) is used for the outer carbs as well as the center cab.
But, in Delco Rochester Bulletin 9C-627 Date May, 1967 (Replaces 9C-640, April, 1966) throttle body gasket #7015345 (not vented) is used.

I have found my 1966 Tripower GTO starts easier hot with the vented 7015106 gasket, but i´m currently using the closed throttle body gasket per the manual.
What was the reason for the change over to the closed gasket?

And, i have not found info for the direct reason on the .030" drilled holes in 1964-66 outer carbs throttle blades, other than keeping the throttle bore clean from "gumming up"?

Looking forward for your info on the center carbs!
1) The "Vented Gasket" works well in warmer climates as when you shut off the engine fresh air fromt the vented gasket has a "Fireplace/Chimney" effect that lets fresh air come into the center venturi section of the carb, pass upward to the air filter, and then disperse thru the air filter to the engine compartment when the engine is shut off after running. Heat and vapors rise.

With the California Emissions Standards, back in the early 60s, the California Carbs went to the closed crankcase system which basically trapped the fumes from the carbs until a restart and then the fumes were burned. The PCV system also allowed burning off the crankcase fumes. Later they used Carbon canisters to trap the excess fumes.

2) Most times when you add a bleed hole in a throttle blade you are adding a place for additional idle air to get into the carb with the throttle blades in the correct relationship to the transfer holes or the transfer slots.
Sometimes you do this is the engine has a larger camshaft and needs more airflow to idle with the extra charge contamination from the extra overlap.

If you just crank up the throttle blade then you screw up the primary blade/ or carb idle function. 4 tiny .030" holes can add a bit more idle air flow even with the throttle blades 'Dagged" so no leakage around the blades.

I personally think they did it because they "dagged" the blades.

Tom V.

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