My son has a 1979 Evinrude 70 hp on a 17 ft runabout. The motor model number is 70973R and is used in the Ogden, Utah area on lakes at 4500 and 5300 ft elevations. The motor does not idle reliably and stalls soften. When the throttle is advanced, it bogs badly. If you are patient, you can get it to run reasonably and put the boat on plane if you can get it to full throttle without bogging to a stall. I believe that the carburetors need to be re-jetted for use at higher elevations, but I'm not sure which jets need to be changed. There are 3 fixed jets, and I'm assuming that they all meter fuel and cover idle, mid-range, and high speed. I don't have the motor in front of me since I'm in Pennsylvania, my son is a good mechanic with no experience with outboards, but he does follow directions pretty well; I'm trying to advise him to help resolve this issue. I have an OMC manual for a 1980 model motor but there are no references to adjustments for elevation. In the Clymer manual covering this motor, there is an orifice chart with recommendations for different elevations, but it only provides recommendations for the high speed jet. I'm hoping that someone has some experience with this problem and can provide some guidance. This week one of the carbs will be disassembled and the jets will be measured to confirm the jet sizes that are in the carbs right now.
