Help! Car won't idle

Fresh 358cid, SBC, on E85. Holley 4150 Prosystems carb. Have had this setup for about 3 years now. It's always been a little touchy at idle, but this season I can't get it to idle at all. It will fire right up, run for a second or two, then die. But always fires right back up, but also won't ever run for more than a few seconds. Have tried multiple new base gaskets thinking I have a vacume leak, but made no difference. Have tried spraying carb cleaner around the base of the carb looking for leaks, nothing.
Have the idle mixture screws at two turns out currently, but have had them as far in as one turn and as far out as three turns. Makes no difference. Car still fires then dies. Float levels are set so that you can just barely see fuel at the bottom of the sight glass.
What else can I do? What else can I check?

Lowest RPM it will run at is in the 1800-2000 range. It won't idle no matter where I put the mixture screws.

Sounds like the idle air bleeds are stopped up. Try using the little plastic straw on the carb cleaner can and spraying down in the 4 small holes right above the venturis. I think it is best to do this as you are revving the engine, the vacuum helps suck any dirt on thru as you spray it.

Fixed it!

Removed the metering blocks, cleaned everything up real good, sprayed out all the passage ways, installed different size air bleeds, drained the fuel tank, installed fresh fuel, fired right up and ran great.

Thanks for the help.