Thread subject: Whaler Central - Boston Whaler Boat Information and Photos :: 1985 Sport 15 with a Yamaha 70 ELTK...Props?
Posted by onejaboney on 06/22/09 - 8:42 PM
#1
I run this boat at 8000 ft in Colorado and just installed a new 15 pitch prop and it still doesn't plane or rev.
My tach is broken but I wonder if a 11 pitch is what I need?
Some guys at the marina in Grand Lake run a 11 pitch prop on their 40 hp four strokes and they work great.
Any help with tuning for altitude would help.
Posted by Joe Kriz on 06/22/09 - 9:13 PM
#2
You may need high altitude jets.
Talk to your dealer.
Anything over 5,000 feet in elevation most likely needs a jet change or computer calibration depending on engine.
Edited by Joe Kriz on 06/22/09 - 9:14 PM
Posted by theo on 06/23/09 - 7:44 AM
#3
Was the motor sold new in CO? If so it should already be jetted for altitude. If it came from out of state, I agree it could be running rich.
Posted by Tom W Clark on 06/23/09 - 7:56 AM
#4
As we all know, engines loose power with altitude where the air is thinner and there is less oxygen.
At 8000 feet a 70 HP outboard is going to perform like a 50 HP outboard at sea level.
We know that 50 HP on a Sport 15 should push it to about 35 MPH.
I believe the Yamaha 70 uses a 2.33:1 gear ration so with its 6000 RPM redline, that suggests you would need a prop with about 16" of pitch.
If you're running a 15" pitch now and the boat will not go, there is something else wrong.