Living at sea level my 1980 70HP Merc ran excellent. We moved up North and live at approx 3000 ft above sea level. Since then my merc is not reaching full speed like it used to. The engine does not wind out like it used to. Taking the cover off the powerhead used to be like looking at a brand new engine, dry, new looking. Now it has an oily residue on it and when I take the air box cover off the plastic around the carbs are all oily and the throats of the carb is oily. My manual says I should go to a main jet of 0.084 rather the 0.086 that is in it. Plus change the vent size to. Would that make much of a difference?? My plugs I've never changed. I did notice a loose wire on the switch block and since fixed that and it ran better. The #1 plug seemed a little fouled too. All the plugs were soaked in fuel when I pulled them after skiing one day. Like other engines, should the plugs have that nice tan color? I adjusted the idle and that helped. Lately the engine is stalling when you punch it. I don't understand. I figure the elevation change is the problemo. Carbs are very clean since I checked that last season when I noticed the lack of power at WOT. I'll check the compression today.
