Power at altitude

[Willardsco]

I have a 50 hp Force motor, 1989 model on a 17.5 ft boat. At my home elevation of approx 600 ft above sea level the motor runs excellent and will push the boat at app 30 mph. On a lake at 9000 ft elevation the motor will barely push the boat at 5 mph and runs very rough. What can be done to remedy this situation? Thanks for your help.

 

[Big Four]

Re: Power at altitude

I've always understood a 2% hp loss per 1000ft elevation. This sounds more drastic. Anyway the carb needs to be rejetted. Right now she's getting way to much fuel for that elevation. It's a pretty standard change is to find a high altitude mech so to speak.<br /><br /> Be aware, once you rejet her for the high altitude you can't run her with the small jets at lower altitude. She will be running way to lean. This can lead to over heating, lack of lube, all of which will ruin the engine.. With the smaller jets and the thinner air(less oxygen)don't expect her to run like 50hp, more like 30hp should be expected. Dunk

 

[wood]

Re: Power at altitude

Big Four is right. I bought a 50hp Force with a #82 jet - Very poor performance at about 5000 ft. I went to a #90 jet and increased performance but only got about 35hp. performance. From what I can gather, that's about all I will get. Don't forget to change the jet when you go below 3800 ft.

 

[sony2001]

Re: Power at altitude

Willardsco for 9000' go to a 0.078 or less down to 0.076 0n a 1988 50 hp Force.<br /><br />------------------