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2K views 3 replies 4 participants last post by  White Whale 
#1 ·
Im having a problem with my carburator. I recently had to buy an edelbrock because the q-jet quit on me. I tried to find out what cfm size the original carb was but I couldn't. No one at the auto parts store could help me. They didn't know anything about Cadillacs. I found a formula online where you could calculate the size carb that would be right for your engine. It was around 600 cfm, so thats what I bought. I bought the one that is 50 state street legal because I live in Phoenix and emissions here are the same as California. The car I have is a 82 Fleetwood with a 425. To make a long story short Im have problems when I give the car alot of pedal. If I floor it, 5-6 seconds into the pull the engine starts to starve for gas. It surges and when you let off a little it is fine. Did I buy too small of a carb or am I having fuel pressure problems? What was the size of the factory carb on a 78, 425? Can this be fixed by up sizing the jets and metering rods on the Edelbrock? Any insight would be very helpful. I would also like thank TorqueInc. for emailing me pics and info about putting a 500\472 intake and exhaust manifolds on a 425. If anyone is in the Phoenix area and has a 500/472 engine for sale, please email me sdb1177@hotmail.com. Thanks!!
 
#2 ·
the stock Q-jet was 800CFM... so if a 600CFM carb is way to small...

Hoenslty, I would return the Edelbrock, the QuadraJet is one of the best carbs you can put on a stock-mild BB Cad... only when you really tear down the enigne and build it for major performance would I start looking at other carbs...
 
#3 ·
There was only a 750cfm and an 800cfm Quadrajet so either one would not be served by a 600cfm carb. BTW, the formula for figuring the best carb size for given engine is as follows:
CID (Cubic Inch Displacement) times Max. rpm of the engine, times VE (Volumetric Efficiency), divided by 3456, equals the proper CFM size. Use a VE of 1 (equals 100%) unless you know a specific VE you want to use.
So in other words, a 350 cu. in. engine with a 7000rpm limit would use a 709cfm carb.
 
#4 ·
Doing the rods and jets on the primary side only helps with the part throttle circuit.
The secondary jets are a little harder to change, as I think you have to take the hat off.
As mentioned before, the carb is a bit small in box stock form, BUT... the secondary jets can be changed to allow more fuel to flow when you lean into it.
While the Q-Jet is a great carb, I like the ease with which I can tune the Edelbrock Performers, and the fact of no gaskets below fuel level.
Just my $.02
Mike

PS..I think the generally accepted VE for a stock engine is around 85%
 
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