One problem with the G2 carby was the lack of adequate sealing of the butterfly spindle in contaminated air conditions.
The G2 Carby doesn't have both sides of the butterfly spindle sealed off to the outside contaminated air.
The G3 superseded this design flaw by sealing off both ends of the butterfly spindle (the G2 only had one end sealed)
The red circle shows the spindle plug for the updated G3 carby in the image below.
The G3 patent was lodged on the 31st of March 1970 so the G2 was used for more than 12 months.
I would say the throttle control was improved with the G3 carby looking at the two different designs.
Not sure why there was scant reference to the G2 carby in the 68/69 manual.
Every mower I've had that should have a G2 was retrofitted with the G3 so I can't report on other bad characteristics other than the ones I have mentioned.
A few Inventors names listed on the below patents.
