Small third port motors are very sensitive to piston to cylinder clearance. fifty to one oil mixes are a real killer on those low horsepower outboards. A few thousandths ware on a PO or Speeditwin is inconsequential as a percentage of the large bore. But on the smaller motors it is a much larger percentage. Some are improved by using a low ash SAE 40 weight oil. This usually requires a hotter spark plug. Tinning the bronze bushings with lead free solder (Contains silver) can eliminate excessive crankcase pressure loss through the bearings. In some cases judicious use of a tail pipe expander can add a thousandth or two to the base piston diameter to decrease crankcase pressure loses. Some early outboards added a piston ring to the bottom of the piston. Modern practice uses closer tollerances for this seal.
