shocktower has it right. the suspension in 1980 was an improvement over the earlier model, but they still didn't have it right. suspension is everything on this model. if you can make the rear shock work for you, it's a very competitive bike (although the it200 is light years ahead of it handling and motor wise)
if it was mine, i'd find a 43mm front end from a 81-85 (can't remember exact years..) yz250/it or bigger and throw it on there. gold valves work well in the stock or in the 43mm front end. springing the front for your weight is crucial either way - most ITs are pretty under sprung (unless you weigh 140lbs..). once you get the front end worked out, i'd concentrate on making that rear shock work. - definitely check all swingarm bearing/bushing for wear.
that motor is bulletproof.
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