bandit 6's and 12's are favourite for playing with and they are usually bullet proof, which is why they keep their values. I work with a guy who bought a 6 from a collegue 15 years ago and its still worth the same today.
the problem is, being easy to play with means its easy to f**k up.
sprockets are usually a second thought but occasionally do get played with, sometimes as a result of fitting raising or lowering kits.
could have restrictor kits fitted , there might even be a throttle stop fitted, mainly due to qualifying for cbt riding.
one thing is a possibility , being 20years old the diaphragms may be starting to perish, resulting in the vacuum that lifts them at full throttle opening wont stop them dropping. while the lids are off, (to check top hat restrictor as opposed to inlet disc restriction) gently pull the rubbers apart at the folds, any sign of daylight could be a problem.
finally, one problem was , later ones were fitted with carb heaters to prevent icing, if these are not working you could be back to icing again.
oldest had 3, youngest is on his 4th and his mate on his second. personally having worked on far too many in the business they are Suzuki's and I was Honda all the way.
