i have a brand new honda GX390 13hp engine. i managed to get it for 100 dollars . it really helps to know people. but i was wondering what all can i do to it to make it faster than stock. and i dont want to be buying new cams and cranks and rods and suck. just cheap stuff or little tweaks here and there. anyone got any suggestions?

methanol carburetor, bettter head, better coil for hotter spark, hotter plug, better oil... ect