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ive got what i assume to be a spread bore quadra-jet carb on my cadillac 472. i was thinking about putting a square bore 750cfm edelbrock on with an adapter. before i go spending that money i was wondering if anyone had any input on this swap. im also considering swiching it over to a manual choke.
 

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Been down this same road with a 472 Caddy in a '40 Buick. I was having problems with the QJ boiling back the gas after the engine would sit for a couple of hours. Had it rebuilt twice. I could start up within about 30 minutes of shutting down, or wait overnite, and it was fine, otherwise, I would have to grind several revolutions and it would finally kick off, and the black smoke would roll out the exhaust. I changed to a 750CFM Edelbrock w/electric choke with the correct squarebore to spreadbore adapter, and cured my problems. I found that the low intake on the Caddy would create heat and boil back the gas in the carb and flood the engine as well as evaporating all the gas from the carb after 30-40 minutes. This was causing my problems. The Edelbrock and adapter plate gave me the distance from the intake and the heat sinc needed to eliminate this problem. I changed to a small block Chevy and a 600 Edelbrock and used a phenolic block spacer to achieve the same results. Don't know if will cure your problems, but it worked for me. You might try a phenolic block spacer between the carb and intake if your QJ is in good shape, if not, go for the 750Edelbrock, it works good on this engine.
 

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I myself like the carter 750cfm better than edelbrock, and the carb spacer from spread to square bore is aluminum and can be polished real nice plus it all comes in one convinient kit for $40 bolts nuts the whole shebang
 
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