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You need to raise the pulley ratio to magnify the available engine torque, and that is done with machining, shim and weight selection.
Then use the lightest secondary spring to transfer the torque without the belt slipping.
Measure your roll-out with the stock tires to compare to the new tires to determine the difference in true diameter between the two by ratio.
You have to raise the pulley ratio the same percentage as the difference in tire diameter ratio to get the stock feel back, and several members have raised the pulley ratio more for better than stock low end pull.