A friend of mine has a collection of WR250Z's from 92-97 he even has a 93 WR500 2T which is a ton of fun. 89's were known as the YZ250WR while later years were just WR250Z. Imo they are one of the best 2 stroke dirtbikes of all time even by todays standards. Unlike the YZ they had XC suspension, heavier flywheel with lighting coil, 18" wheel, larger fuel tank, wider gearbox along with a few other changes to make them more trail/xc friendly its really a shame they quit selling them in the US in 97. Unlike a lot of the enduro/xc bikes during the 90's the WR's were NOT detuned in any way shape or form--they rip and are every bit as powerful as the motocross bikes of the time.
My biggest complaint with them is the stock fuel tank on the 94-97's... I don't know what Yamaha was thinking but its like riding with a beach ball between your legs
A good solution (like the later 4T WR's) is upgrading to the YZ seat and aftermarket desert tank.
Imo the later round slide Mikuni carbs that came on the WR's were not too bad. If yours has one I'd try tuning it in first before you decide to bail on it. The earlier models had the flat slide TM which is a total POS. That said the PWK is an upgrade to anything Mikuni imo