rich idle

[c413]

AirFloat IHave A 72 Cuda With A Indy Headed 408. TheCar Runs Great Except At Idle. The Carb Is 4150 Holley With 4 Corner Idle. The Idle Mixture ScrewsSeem ToHave Little Affect OnThe Tuning. I CanScrewThem All TheWay In And TheCar Still Runs. ItHas A Comp Thumper Camshaft In It. I CanOnly Tune About 10In. Of Vacuum Into It. I've Changed The PowerValve, Checked float Height, I've Changed Primary Side Idle Air Bleeds, I've Drilled A 3/32 HoleInThe Front Blades, AndOpened The Rear BladesUp To Expose More Transfer Slot. I've Installed A Gauge And regulater AndSet The Fuel Pressure To 5Lbs. IDon't Know What Else To Do. Its Fouling Plugs. PleaseHelp.

[jhaag]

The transfer slots should never be exposed at idle. Will cause excessive richness at idle.  Close the blades both front and rear to the bottom of the slots. The motor is telling you it wants more air at idle. I would drill holes in the secondaries as well. Keep the holes the same size front and rear. If you have adjustable air bleeds you can also work with them. Another old trick is to put some fine wire inside the idle fuel passages to restrict fuel volume at idle. I think you will see a huge difference by closing the throttle blades and drilling holes in them. When you have this correct, your idle adjustment screws will then work as they should.

[73EStroker]

You may have idle feed restrictors inside the bowls of the carb. They look like a bunch of jets in a vertical row if you have them. you only need to change one at a time and you will need the blue gaskets as you most likely will have to remove the carb bowls a few times. You can reduce the size of them which restricts the amount of fuel available for idle. Best bet is to find (if you can) some old carb guy but those people are dying off. I had this problem and believe it or not ................. it was very restrictive POS Cherry Bomb Turbo mufflers causing the problem. Put Magnaflows on and the rich smell has gone and the performance is out of this world now!
I base this post on your carb being the same as my Proform 950 which is adjustable everywhere. Holley make very much the same product.