While sat having a pint of Coke, and some grub down the pub myself and Andy got onto the subject of piston weight. So for those interested here are some figures.

All figures are piston complete with rings, wrist pin and circlips

HRC F3 piston : 162g (no it wont fit a stock crank)
MC21/28 piston : 201g
Tyga 300 piston : 227g (yes it will fit your stock crank, no it wont fit your stock bore ).
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If I have to take the carbs off once more...