Re: XP 1987 100 hp
It would be helpful to know the model number off your engine. I don't see an XP100 for the 87 model year. OMC did make a 100 hp engine that year, but it was a commercial engine, not a "normal" consumer engine. In 88 and 89 OMC made the XP100 model. It had some fancy decals on the side, but was very similar to the 90 of that year. The carb jets were larger in that 100 than in the 90, so likely it did put out 100+ hp. It is typical that the XP models have extra cowl vents for better airflow, so your model should have extra vents at the top/back of the cowling.