Success!
I pulled the carby & blew (or sucked) it out. Re-installed and found that the governor spring was hooking on the throttle lever. I bent the plate upwards at the cable end so that the governor spring clears the throttle lever which now opens all the way. No more cutting out or limited revs.
I also picked up a Wolf mower with Briggs 2 stroke motor for ZAR400. The chassis is not so hot, but the motor runs perfectly.
