Carburetor too big, too small or just too rich?

I would sure appreciate some guidance on which way to go with my carburetor trouble.

Ive got a 1970 Skylark custom convertible 350-2 with AC. I decided to upgade to a four barrel intake and carb and dual exhaust for better performance and I hoped a little better MPG's. I got an old Buick iron 4 barrel intake and replaced the single exhaust with 2 1/4 dual exhaust with X cross over. Then, based on a recommendation from Holley, I got the Holley 4175 Quadrajet replacement 650 CFM carburetor part number 0-80555c. I also got a Holley idle solenoid to kick up the idle when the AC is on.

Since putting on the new Holley and 4 barrel intake, the car is running too rich. The plugs keep fouling and when I start it up, the tailpipes put two big black circles on the ground!

A highly recommended local mechanic tells me the problem is that the Holley is too big for the engine. He says even though the Holley might be correct for a Buick engine that was originally a 4 barrel, my stock 350-2 engine has a different cam and probably lower compression and needs a smaller carburetor. He recommends around 500 CFM. Someone else with a lot of Buick experience says the Holleys just metered way to rich and needs rejetting. He says the original carb for my engine would have had 750 CFM.

Any opinions out there? Is my carb too big, too small or just too rich?

Thanks!

 

I won't pretend to be a carburetion expert, that I'm not, but I'm certain beyond a doubt that a carb that's too large for an engine won't idle rich because of that reason.

I'm not too familiar with Holley's, but it sounds to me like maybe the power valve or metering rods are stuck full rich......are you certain they are getting a vacuum signal? That happened to me once and it was because I used the wrong base gasket. :bglasses:

 

stock buick 350 engines came with 750 cfm quadrajets so your 650 is not to big. the 2 barrel heads are the same as 4 barrel heads and even the later low compression buick 350 engines used 750 cfm carbs. check the float level it may be to high causing flooding at idle. have you set your idle mixture adjustment yet?

 

What Bob said.

650 is not big enough for a Buick 350, so something else is causing the problem. You can check the choke too, make sure its opening all the way.