I am building a horse walker. My motor is 1750 rpm's. The pulley on top of the gearbox is 5 inches. From gearbox to main drive gear is 4 inch pulley on gerabox to a 16 inch pulley on walker drive. I need to know what size pulley to put on motor so walker won't be like a carnival ride and go too fast. I am thinking about using 1-1/2'' pulley on motor. Is that too small?

Hi,
Well, to you have a 5:4 ratio on input and output with a 1:4 ratio on the walker drive. Total reduction of known parts is 0.2:1 and would yield an effective RPM 350 with a 1:1 ratio off engine.
Unknown quantities are the ratio within the gearbox and the diameter of the wheel/tire combination on the walker. I gather you do not wish to experiment, so all info is needed.
Peace,
Clarke