Bob,

Per Jon's (carbking) earlier reply to your questions:

Originally Posted by carbking
Unless the engine is either just rebuilt (less than 500 miles) or almost worn out (burning a significant amount of oil), then 3/4 turn to 1 turn on the idle mixture control screw is a good starting point.

1 1/4 turn will probably SEEM to idle more smoothly, but waste gas at idle, and foul plugs.

Jon.

It sounds like instead of decreasing the idle mixture setting (you said it was previously 1-1/4), you have instead increased it to 1-1/2 which may lead to some of your falling flat issues.

That being said, there are may variables that could be causing your issue. You mentioned you rebuilt the 2100s. Did that include a complete disassemble, cleaning and blow out of all ports and orifices?

Beginning to wonder if their is a blockage in your carb somewhere affecting your operating circuits beyond the idle circuit.

Just in case it may help, here's a link from "carbkings" site Carter YF Service that may be of some use in understanding your carb.

~ Dan
1951 Chevy 3 window 3100
Follow this story in the DITY Gallery
"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)