Idle issue with 63 chevy

[Mack B]

Ill try to be as detailed as possible,I'm no mechanic, but have been around old piles of crap all my life and can handle most tasks under the hood. the weather here is in the low 70's and has been every time I've had the truck out. it's a 283 small block with unknown internals but runs fine on 87 octane usually has a mild lope when it's cold, edelbrock 600cfm carb, and summit hei ignition. It's been running fine till the last time I drove it, it was idling rough (sounded good really ) but the idle speed was low and tried to die just off idle. This was last weekend, this evening I had a chance to mess with it, I tried turning the idle speed up, but it would not increase. After turning the screw if I patted the gas the idle would stick high for a few seconds then fall back low. After that failed I richened up the idle screws a bit and that helped smooth it out a bit. I then adjusted the timing from 8 degrees advance to 6 degrees at idle (made no difference). It did get warmwhile i was playing with it around 195 degrees (i know this is no where near over heating, but the highest ive ever seen the gauge scince ive had this truck is 180 in the middle of summer) My question is did I mask a problem by fattening up the idle mixture? What would cause it to need to be adjusted out of the blue? Anything else that would cause these symptoms I should check?
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