Just replaced intake gasket and two head gaskets(due to broken exhaust bolts in head). Before I did all the repairs, the car had a flubbing and stalling out at WOT...it just backfires, pops, and then dies. Runs great at idle and when you accelerate up to WOT. I have gone ahead and rebuilt the carburetor replacing all gaskets, jets, cleaning all ports, accel pump, everything. This is Rochester 4bbl. STILL HAVE THE ISSUE AT WOT after rebuild. I seem to remember this happening on my 70 Skylark w/455, 76 Electra w/455, and now this 72 LeSabre with 455. All had 4bbl. Is this just nature of the beast with OE carb?
How old is your fuel pump? I would replace it and all the rubber lines with fuel line compatible with ethanol.
Fuel pump and all lines are less than a year old...issue existed before replacing pump and lines. If it is running lean, what am I adjusting...idle mix screws? Spark plugs are fairly clean and slightly brown...not powdery which means lean...right?
Wrong, the idle mixture needles increase or decrease the volume of mixture added at the idle discharge ports. The idle mixture is determined by the internal calibrations inside the carburetor, that are not user adjustable. The only way to really know if you are running rich or lean is to use an O2 sensor. It does sound like you are going lean as you approach WOT though. I would plumb in a fuel pressure gauge and see what is happening at WOT. New parts are no guaranty. They can be defective right out of the box unfortunately.
