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Author Topic: modify or purchase correct carb  (Read 2034 times)

Offline Tom Lynch

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modify or purchase correct carb
« on: September 15, 2012, 07:44:26 AM »
I have a 1971 Buick GS with a non original 1970 455 engine. The carb on the engine is a 7041544 which is for a 1971 350 engine. The car seems really lean when the secondaries open up, i get some detonation if i stand on it hard. My question is should i attempt to re work the 350 carb to work with the 455 engine or would i be better off with the correct 7041540 carb and just rebuild that to factory specs? I don't know much about the engine as it was already rebuilt when i bought the car but i have been told that is is essentially stock with a mild cam (  218 intake 224 exhaust .490 lift) the car pulls 16 inches at a 700 RPM idle. 
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Offline qjetsrule

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Re: modify or purchase correct carb
« Reply #1 on: September 15, 2012, 11:59:31 PM »
TOM, YOUR CARB IS A CALIFORIA EMMISIONS MODEL, WHICH MAY BE TOO LEAN FOR A STOCK 455. I THINK A CALL TO CLIFF FOR A CORRECT REBUILD KIT MAY BE IN ORDER, DON'T FORGET THE IDLE TUBES. BUT ALSO CHECK YOUR DISTRIBUTOR TOTAL ADVANCE, WITH TODAY'S GAS, I'D LIMIT MY TOTAL TO AROUND 36 DEGREES. A 1970 BASE 455 IS 10:1 COMPRESSION. TODAY'S DOESN'T HAVE THE OCTANE THEY DID BACK THEN. ALSO WITH THE ADDITION 10% ETHANOL IN THE GAS, MORE FUEL IS REQUIRED THROUGHOUT THE CURVE. GOOD LUCK
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Offline Tom Lynch

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Re: modify or purchase correct carb
« Reply #2 on: September 16, 2012, 07:55:37 AM »
Thanks for the input, i have no problem with detonation on the primaries its when the secondaries open up that i get the detonation. I doubt the car is actually at the advertised 10:1 as there are still factory stampings on the block deck which tells me that the deck surface was never cut and the compression is really about 9.5:1 at best. I'll try to adjust the timing but i know the secondaries are lean and the carb will need some work on the secondary side.
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Offline Cliff Ruggles

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Re: modify or purchase correct carb
« Reply #3 on: September 17, 2012, 05:13:05 AM »
Richening up the secondary side takes seconds.  We have richer metering rods available.....Cliff
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Offline Tom Lynch

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Re: modify or purchase correct carb
« Reply #4 on: September 17, 2012, 02:24:14 PM »
Thanks cliff I am out of town this week but i would love to talk to you about your suggestions for richening the secondary side of my carburetor. I have no idea how it is set up now, would i need to actually pull it down and see what hanger and rods i have in the secondary before we talk?
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