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Author Topic:   High altitude adjustments

davidgarth posted 06-05-2001 10:21 PM ET (US)
I will soon be boating at 5300' with my Whaler and a Mercury 40 4 stroke. Do most of you knowledgeble Whalers adjust or re-jet your carbs for high altitude, change props, or just leave everything the same?
Thanks!
Dr T posted 09-17-2001 10:52 PM ET (US)
This is definitely a "Your mileage will vary" question.
My comments apply to my old two-stroke, and 4 strokes, especially EFI, will be a different matter.
After one season with my 82 Johnson 35 HP, I think that I have been able to conclude that it really depends on your specific use.
Props:
I have a 10 x 13, 10.5 x 11, and 11x9 Props.
At very High (> 7000 ft), I believe that the engine needs the 11 x 9 with any kind of load. I also use it at about 5500 ft for pulling kids on a tube, but the engine will over rev (5800 rpm) at WOT if I am solo. Heck of a hole shot, though.
At moderate altitudes, I expect that the 10.5 x 11 will be the workhorse.
ReJetting: I haven't done it, but am sorely tempted to have a mechanic look at it this winter. The motor definitely loses power at high altitude.

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Author	Topic: High altitude adjustments
davidgarth	posted 06-05-2001 10:21 PM ET (US) I will soon be boating at 5300' with my Whaler and a Mercury 40 4 stroke. Do most of you knowledgeble Whalers adjust or re-jet your carbs for high altitude, change props, or just leave everything the same? Thanks!
Dr T	posted 09-17-2001 10:52 PM ET (US) This is definitely a "Your mileage will vary" question. My comments apply to my old two-stroke, and 4 strokes, especially EFI, will be a different matter. After one season with my 82 Johnson 35 HP, I think that I have been able to conclude that it really depends on your specific use. Props: I have a 10 x 13, 10.5 x 11, and 11x9 Props. At very High (> 7000 ft), I believe that the engine needs the 11 x 9 with any kind of load. I also use it at about 5500 ft for pulling kids on a tube, but the engine will over rev (5800 rpm) at WOT if I am solo. Heck of a hole shot, though. At moderate altitudes, I expect that the 10.5 x 11 will be the workhorse. ReJetting: I haven't done it, but am sorely tempted to have a mechanic look at it this winter. The motor definitely loses power at high altitude.