I have a near mint RZ500 I purchased new in 1985. Still have it.

Hopefully you changed the air filter before startup. Yeah, the carbs need a mechanical synch and then vacuum synch. If this thing has been sitting for years warn your customer that the crank seals may have dried out creating an air leak. The engine should get a complete rebuild with all new seals, gaskets, and orings. A bit of hard riding and he may be quite disappointed when the engine seizes up due to said air leak. Good job getting it fired up. At least you know it is capable of running.

Thx for The tip. Have The same problem with mine..overflow from The carbutators

cleanic it after you put it together, no compressed air on a dirty bench? real hack job. when to have rounded a bolts head,tap a torx socket/bit in it,and turn it loose without drilling.

Two strokes are supposed to be simple to work on. Yamaha lost the plot with 500lc, the 350 ypvs was such a better bike.

RZ not RD