The 80's do come up pretty easy, I think easier with an adult on them than a kid. (center of gravity being higher makes that a reality.) the first thing i would do is get your preload or as some call it "race sag" setting right. (race sag just sounds so cool, everyone says it!!) you can easily change the rear spring preload pretty easily. most people are happy when the rig settles down with the rider onboard with about 25% to 33% of the total travel used up. if you dont have anyone around to help you through that the first time, and a manual, get back on here.
next on the cheap list is to see how badly worn your sprockets are to begin with. if you need them, now would be a good time to play gearing games. I like the idea of lower gears for tighter trails, but you may find you have acceptable or even great gearing for your type once you get used to the bike, have your riding position down (sitting leads to wheelies). if you have the weight on the pegs and are slightly off the seat with your elbows turned up the bike will track better under throttle and stay down more.
finally if you want the engine more suitable for trail consider getting a kx 100 cylinder (pre power valve) for yours or simply have your worn cylinder bored and plated (you will need the head milled out to fit the new piston too) to accept the piston from the kx100. it is really all kawasaki did in building that one. boring it out as far as they did without restoring the port timing and keeping the same carb as the 80 made the bike slower and easier to ride.
Boring alone retards port timing btw.
Flywheel weights are nice too. We have built them up to 40 oz and even put them on yz80's and kx100's. you can get some more resistance to stalling by going to one of the bolt on weights, but the weights avail didnt do as much as we wanted.