I have a 1977 or 1978 Johnson 175 hp. I am using a 14 1/2 X 18 prop. The powerhead was rebuilt in FLorida years ago but the engine does not have 100 hours on it. I live in Colorado and had it jets put in for high altitude. Today the boat would not start until I got back home. <br /><br />Now to explain. The boat runs fine at Lake Powell, aproximately 4000 feet in altitude. I live at 7000 feet and the resevoir (Ruedi) is 7800 feet. Got the picture! <br /><br />If I can get this running up there it often stalls at hole shots and often just bogs down. I am thinking jetting problem here. I can't find a chart that will tell me what size jets I need for this altitude. I would like to be able to run between 4000 and 8000 feet. <br /><br />I believe I have a 59C jet size in it now. A mcechanic told me I need 54C in this engine for this altitude. He sold me three. When I got home I was told that I need 6 jets. <br /><br />My question is what size jets should I use for this altitude, mostly 7800 feet, and how many do I need? Oh and where the hell on the net is the chart that I am looking for?<br /><br />Thanks