Re: 1973, 85 hp Ev. power upgrade?
The 85 is basically a de-tuned 115, for marketing reasons. By the time they stopped making them, they were even the same displacement as the 115-140hp (1979-80 were 3.5" bores). The easiest thing would be to bolt on a pair of 1 5/16 venturi carbs from a 115-135. GUESSING, I'd figure you might pick up 50% of the difference with just the carbs. The other major item that's different is the porting. That's probably not worth going after, considering it'd take a complete teardown. The carb swap is easy.<br /><br />I've run both (pre-1986 85hps and 115s) on the same test prop, and can assure you the 115 does have more top-end ponies. The 85 turned 4800, sounding good. The 115s turned 5350 and 5410, and everybody else stepped away from the boat ramp (sounded quite a bit hairer). On the boat, the difference is not as noticeable.<br /><br />As DHadley would say, before you sink too much work into the powerhead, you might play with the setup some. You want the motor as high as it can go on the transom, without losing water pressure or cavitating on turns. This itself can speed a boat up a lot. Then prop it so that you're at 5500-5800 with you alone in the boat. If you do a lot of skiing (or party with a boatload a lot), you might prop it even higher. A clean (no dings) prop can make a big difference, if your present one is all bent up.<br /><br />Be sure your motor's healthy before pushing any of this very hard (good compression on all 4; clean, fresh gas & carbs; WOT timing set correctly; decarbed). Once done, I'd find a set of big carbs ($15), & wouldn't mess with an old motor like that otherwise.
