Peter,
I cheated on the "exam". Being an ex-UK Pat living in New Jersey, I actually knew where Australia was.

I am interested, was it the pump side of the cam that failed? (namely the inlet-valve side). The problem could well be that the pump pushrods etc are creating too much drag.

Also I did modify mine in two ways. I recessed the plug 1/16" to stop the injuector from dousing out the glow-plug. This allows a richer run and even a plain clunk and tank with air bubbles could/would not kill the motor. (I have that on video BTW)

The second mod was to make an air-filter that went inside the carb throat to replace the restrictor. This filter had a 1/16" wall and gave very good power with better fuel consumption.

I'm rambling - must sleep... Nite all!