Right now I am running an Edelbrock 1040 (500CFM) with mechanical choke on a 283 SBC. It runs rich most all the time and bogs down off the line. I talked to edelbrock Tech Reps at Columbus & was told I could never get that carb to lean out with a 283 & that I needed to switch to a Holley 390 cfm for best performance. He said the 283 could not flow 500 cfm.
Does that sound right?
What type of problems are there with those carbs?

I have a 390 on top of a chevy 229 v6 only because the Edelbrock 500 CFM couldnt be leaned down enough. The "tech" at Edelbrock said it was fine for 265 cu in and up.
The model is a 4150/60 and has vacuum secondaries. I got close with the jet/rod kit but not enough without it starting to pop and make other assorted noises. Now I'm beginning to wonder if their "techs" work from the same page or by the phase of the moon....BTW, the .052 jets that came with the 390 CFM (actually #521's)were too lean by at least 4 steps so go figure...I've never heard of a 283 not being able to work with a 500CFM carb unless it was bone stock. Fred P
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Fred P.

I had a 500cfm AFB on a 283 Impala. It was a little rich, but ran good. I tried to go a step leaner on the rods and it ended up starving off-idle. I'de take it in for the emission test and it would shoot chunks of carbon out the exhaust when they got on it, but passed alright.

You can also change the springs for earlier/later cut-in point of the rods.

full race 283 breathing at 100% efficiency at 5000 rpm 409cfm

street 283 more likely to breath at about 85% efficiency at 5000 rpm 348cfm
3000 rpm 209cfm

Holley 4150/60, power valves blowing out on the old ones, the newer ones have a check valve that protects them. Vacuum secondaries probably more streetable, usually the 60 is vacc and the 50 mechanical.

I was able to tune the 500cfm to where it ran great, but just a touch rich with the right rods/springs.

Thanks guys.
Right now the 283 is stone stock except for the Performer manifold & carb. I plan to put in a 327/300HP cam this winter plus a B&M torque converter for a little more off the line.
I have not been able to lean out the Edelbrock with several rod and/or spring changes. The guy following me on the Columbus tour got wet black soot on the front of his car every time I jummped on it. That tells me that I am quickly wearing out my rings by washing the lubricant off the cylinder walls every time I accelerate.