Suspension tuning depends on a few variables , Abilty , terrain , riding style and body characteristics. Depending on what you ride , where you ride , how you ride will greatly impact upon setting your suspension up.
The yz's are preety lightly sprung bikes , there's been a BIG difference in valving specs and fork cartriges between the years in which you stated. You would have to be a bit more specific about what bike you have bought.
I'd be taking a flat head screw driver to tune the clickers after a few rides to see how adjustable you suspension is , if you can get it to ride decent you dont need to take it to a suspension specialist to get it sorted. You can spend a motza on suspension work - ie gold valve , springs , shimming , tuning , getting the right oil's in there. But I'd really be trying to tune them up with the clickers first before doing any of that shit.
It takes a while too , back in the day on my 85 I had a fair few problems getting the forks dialed in. Turned out the revalve and use of race tech gold valves sorted all my issues.
Good idea to pull the cylinder off the yz when you buy it and give it a new lease of life with fresh rings or even a new piston kit. Because the 125 rev out quite quickly , have 0 torque your always up the guts of them so top end rebuilds are high on the list. Keep your sprocket bolts tight too , they always seem to come loose on these high reving , viabrating machines
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