Old 05-31-2024, 12:12 PM
ponchorob ponchorob is offline
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Join Date: Aug 2007
Location: Austria vienna
Posts: 315
Default 389 vers 421 tripower center carb

...i know the 421 center carb has bigger design inside the carb vers a 389..... idle tubes ,idle airbleeds, downchannel restriction and maybe some other differencies too.... so the centersection different too ... so in my point of view a lot difference .....so when i want to put a 389 center carb on a 421 theres a lot to change .. what i dont understand even on mike wassons tripower video he only make mods to the cluster dont even touch the center section only the cluster and here ....only make the idle tubes bigger and idle mixture screw holes nothin else ...interesting that this mods are enough what do you guys think....

Old 06-01-2024, 12:06 PM
Dick Boneske's Avatar
Dick Boneske Dick Boneske is offline
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Join Date: Mar 2004
Location: Winneconne, Wisconsin
Posts: 5,407

The Tri-Power center carb body on the 389 vs. 421 is identical. The differences are in the venturi cluster (idle tubes, Idle bypass restrictors, and idle vents), power valve spring pressure, and throttle body idle adjusting screw holes. Keep in mind the automatic carbs had a hot idle compensator on both the 389 and 421. These automatic float bowls are different from the manual trans float bowls, but venturi sizes are the same, 1 1/4".

Any deviation from the stock camshaft will require modifying the areas I mentioned above. I have done hundreds of Tri-Powers, so I have a handle on what is required.

If you need more info, PM me.


'64 GTO Tripower Hardtop (Wife's Car)
'64 GTO Tripower Post Coupe (My Car)
'99 Bonneville SE Sedan
Old 06-01-2024, 02:34 PM
Kenth's Avatar
Kenth Kenth is offline
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Join Date: Feb 2003
Location: The Kingdom of Sweden
Posts: 5,510

What year?
In 1966 389 and 421 Tri-Power uses the exact same center carb, #7026074 for A/T and #7026075 for M/T.

1965 and earlier is another story as Dick describes.

YouŽll find some info here:


1966 GTO Tri-Power
1970 GTO TheJudge
Old 06-01-2024, 02:49 PM
ponchorob ponchorob is offline
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Join Date: Aug 2007
Location: Austria vienna
Posts: 315
Default Carb

Its s 64 center carb,.


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