My brother used to keep a pair of rebuilt VW engines on hand, a 1200 and a 1600, he always test ran them on a hand torch LP bottle. He would sell or loan a motor while he rebuilt the one from the car. We could swap a motor in 45 minutes, less of we had done it before since we made self-holding bolt heads for the bellhousing.
I did get the Kawasaki running, #4 pipe was cold so I swapped the plug with #1. The #4 thread was boogered by a PO and it's a challenge to start it correctly. The pipe didn't warm up much and #1 is fine so I'm guessing it's a float valve issue, RPM didn't help much so maybe it isn't just the pilot jet.