Thanks Bert. yep, I remember motorbike gearboxes and those initial engaging dogs from my earlier days. A sort of syncromesh, hey ?
I think in this Mowcart/ Weedeater One design, the manufacturer doesn't want you moving a rotating vertical friction wheel on the input shaft across the face of the horizontally rotating face of the friction disc on the bottom of the engine belt pulley, unless you put the' clutch' in and separate the two.
I think the speed selection notches alter the gearing, so to speak, by moving the friction wheel from, eg. the centre of the friction disc towards its outward circumference.
In some ways I'm impressed with the design, but generally, its not made to last or to be adjusted. Pity really, as grease nipples and chain tensioners are not space technology and not costly in mass production !
I double checked the orientation of the motion selector handle and as you deduced, it was correct in the first place. It will certainly have tension in the selector slots !
Thanks again ,
Don