I think the problem is when using a standard Power Torque motor with the v belt drive, the drive pulley is smaller than the driven pulley meaning the blade plate is no longer spinning at a 1 to 1 ratio ,this would slow down starting momentum and would require adding a little more weight to the crank to over come the kick back problem.
As we know the 460 Pro motor starts without a blade plate because the boss is heavier than the standard PT boss , looking online the Victa self propelled boss looks to have more weight too ,I guess this is the same boss for the 600.
