Hey @rhodes5150,
Nice early example which should hopefully be full power.
Best thing you can do with these is to start by getting them full stock. That's a derestricted CDI (yours sounds like it should be), then making sure you've got a working YPVS system which is setup correctly.
If the engine is sweet, then leave it alone for the time being. If it's aged and worse for wear, then getting it rebuilt is the way to go. These engines are incredibly simple and easy to rebuild with no specialist tools required. Can drop the bearings in by using a conventional oven heating the cases up.
Checkout Yamaha DT 125 r derestriction to see what's needed for your bike.
Once you've got the stock motor running sweet, and you still want more power then here are a list of mods I'd do (haven done most of what can be done, experience tells me this is the best order and bang for buck).
Exhaust System
Full DEP system
Really perks up the mid-range punch
Cuts out significant weight over the stock system
Zeeltronic Ignition System
Over my DTRE/X (pretty restricted CDI) really punches up the midrange
Carbon Reeds
I run VForce4 Reed block on my DTR
But generic carbon reeds can help
Mileage may vary I'd struggle to tell the difference
Porting work
Making sure the head/squish is correct is where you'll get the most gains
Cheap to get someone to do and can make or break a two stroke
Having the cylinder done can be more expensive and mileage may vary on this
Athena 170
I've grown to appreciate the 170 kit
It doesn't compare to RS 125 big bore kits or other extreme setups
Massively increases the mid-range (reducing overrev)
Makes the ride much easier to live with
Of course this can also be ported to make additional gains here.
You can do other mods, such as skimming the flywheel. This doesn't give you any more power per se, but allows the power to be obtained faster. This can drastically affect the overall performance though, so sometimes it's best to leave it alone.
