I picked up a 90's tohatsu 9.9 longshaft as-is with no history (same basic engine as M15, and also nissan 9.9hp, 15hp, 18hp) and did a tune up incl. new plugs, impeller, gear oil, and a full carb cleaning.
I am running 50:1 quicksilver semi-synthetic oil and new gas. The oil is measured...