Demon carb on 289???

[69roadrunner]

Hi. This is my first post.

My neighbor asked me to help him with his '65 Mustang coupe today. He has a 650 vac. sec. Street Demon carb on a .040 over 289 and it is obviosly running rich (black smoke at idle). I told him that I thought that carb is too big for a 289.

It has a 284 adv. int. dur. hyd. cam (sounds healthy), high rise dual plane, aftermarket c.i. heads with 1.94 intakes, headers, crane ignition, and 10.5 to 1 slugs. It is pulling 11" vac. @ 800 rpm idle so I left the 6" power valve in. It seems to be jetted close as it does o.k at half to WOT.

The carb has four corner idle set up. I have each screw turned out only half turn and it still smokes and smells rich but not as bad.

Is the 650 too big? Should he go to a 600? Also, I turned his total advance up to about 34 degrees and it seemed to like that under load. Is that about right for a mild 289?

Sorry for all the ?'s but my hobby lies with Mother Mopar.