i tink the effect of lightened pulley is almost the same as lightened flywheel.. easy to accelerate but will come to stall fast oso bcz of reduced moment of inertia.
besides changing the pulley, i hav heard ppl adjust the angle of the pulley sprocket....by a small angle,mayb 5deg,so that spark will come earli and combustion happens earlier,which wil avoid power loss. From an automotive book that i read,spark naturally should be out before the piston reaches its TDC(top dead center) / when compression stroke occurs.