AS;
Don't take this wrong, but where do I start...based on what did you change Metering Needles and Damper oil viscosity?...if for any reason less than full range dynamometer motor tests, where engine response and exhaust gases are checked under all load (steady-state and transient) conditions, I expect that explains half of the tuning problems...
From:
https://www.sw-em.com/su_carbs.htm
"...this is exactly why wrong Metering Needles get into carbs: ...he says: "...you can kinda look at the chart....I think I'm going to go to an XXX needle". What kind of a system for picking a needle is that? None! Metering Needles for a particular configuration of engine (mostly influenced by camshaft, manifolding - intake and exhaust flow) were arrived at after countless hours on a manufacturer's motor test stand (dynamometer), running at various RPMs, loads, throttle settings, and with exhaust gas analyzers... very few casual mechanics or even shops are equipped enough (mentally or hardware) to get this any better than the factory!...but they think they are!...so they'll try...and that's why incorrect needles are found in carbs! Do not change Metering Needles unless you can put motor/vehicle on a dynamometer to scientifically check the results...like so! (see Reference: B18 on dynamometer) ...and if you feel the need to change the mixture slightly (for instance seasonably), adjust the Mixture Adjustment Nut only...no more!"
...and Damper Oil should be 20 weight (and because that is what ATF is, and because it has a wide operating Temp range, and is available inexpensively in quarts, it is a popular alternative)...and BTW... Dashpot Drop is
not dampened...only Rise!
I doesn't surprise me that you gave up in the end and went to Webers...I wonder how that went...
Cheers