Hello,
Something that I do when I acquire a machine where the maintenance history is unknown, or foggy at best, is to cover off on the basic maintenance items.
A lot of these machines received little, if any, TLC throughout their life & considering their age they could use a little help.
Engine: Compression test(leak down test preferred). No sense trying to tune or repair a damaged or weak/worn out engine. Install new spark plugs.
Fuel system: Drain fuel tank & clean inside if needed. Remove & completely disassemble carbs for a proper cleaning(not for the novice). Document carb calibrations(jets, needles, air / fuel screws, etc.) Assuming the machine is stock verify if those calibrations match the OEM specs. for your machine & altitude / temperature. Replace fuel filter, fuel lines, impulse line to fuel pump, etc.
Clutches: Remove, clean, & inspect(not for the novice) Replace worn bushings / buttons, confirm proper spider button to tower clearance, confirm proper belt to sheave clearance. Document clutch calibrations(weights, springs, helix, secondary spring position, etc.) Assuming the machine is stock verify if those calibrations match the OEM specs. for your machine & altitude / temperature. Install new belt & shim secondary clutch for proper belt deflection.
Chassis/suspension: Drain chain case & inspect internals. Document gearing. Assuming the machine stock, verify if the ratio matches the OEM specs. for your machine & track size / altitude. Inspect all suspension / steering components for wear &/or proper movement(I.E. seized cross shafts for rear suspension pivots are common) Ensure condition of track drive shaft bearing(this lube point is missed by more owners than not!) Complete grease job.
I do all of above on a used machine before I start fooling around with adjustments. I mention all of this as I've seen many people, myself included, try to tune /adjust a machine to compensate for a mechanical deficiency / lack of maintenance. Along the way if I find settings that are out to lunch compared to the OEM specs. I'll make changes accordingly.
A machine in good mechanical condition adjusted to OEM specs. will run good enough for 95% of the people out there & certainly more than adequate for a sub 100 lb pilot!
Good luck!