low rpms

[hardcase]

A little history, 90 bayliner cuddy with a 90 hp force outboard. Had a shop take a look at it before season, said only running on 2 cylinders, fixed that problem, bad cd box. I have taken the boat to an area lake, 5500' above sea level running an 11 pitch prop, I can only get 4800 rpms, at sea level, with a 15 pitch prop I can get 5200....I am not sure if i have a carb problem or an ignition problem. Shop wants to take it to the lake, for a fee and trouble shoot the problem there..any suggestions before I spend any more $$$.

 

[JB]

Re: low rpms

I don't think you have a problem, unless your wrench thinks he can adjust air density.<br /><br />I would get a shorter pitch prop for the high lake and keep the 11" for low altitudes.<br /><br />Others might suggest a jet change, but it is a lot quicker to swap props.<br /><br />I just returned from a trip in which I had to drop one gear lower than usual to climb grades at 5,000' and two gears lower at 11,000'. A dramatic demo of the effect of thin air.<br /><br />Good luck.