Will 700 feet of elevation affect an outboard?

[hardwater fisherman]

One of the lakes I frequent is around 450 feet and another has close to 700 feet of elevation. I do not feel any difference between them, But when I boat on the St Lawrence river close to sea level it "feels" like I am turning a few more RPMS. I do not have a tach so I can not confirm this. Also if it matters I am talking about a 1976 40 hp evinrude. At what point is changing carb jets needed?

 

[Sea Rider]

That's bare minimum, should see some performance difference at around 3K feet of elevation. Without a tach won't actual wot rpm lose compared to sea level boating. Instalall an induction Hardline hour/tach for that matter.

As load kills wot rpm, worse at altitude, the question is how loaded do you like boating so to choose the right less prop pitch to pull wot revs up for engine to rev at least to middle wot revs when at the highest of both altitudes.

Don't need a high altitude carb kit for such small elevations, just prop engine right for your given usual load.

Happy Boating

 

[Chris1956]

If I remember correctly, Mercury sold jets for 5K ft elevation and above. Below 5K feet, stock jets were used.

 

[hardwater fisherman]

Okay thanks.. I figured 700 feet was not much and was just asking..

 

[Scott Danforth]

the barometric pressure change on 700' elevation compared to sea level is the same as a 5 degree temperature swing. dont worry until your above 5000'

 

[82rude]

No.

 

[dingbat]

One of the lakes I frequent is around 450 feet and another has close to 700 feet of elevation. I do not feel any difference between them, But when I boat on the St Lawrence river close to sea level it "feels" like I am turning a few more RPMS

Humm....sea level means tides.

Do you take tidal effects into consideration when boating on the river?

https://www.tide-forecast.com/locati...c/tides/latest

 

[jimmbo]

If I remember correctly, Mercury sold jets for 5K ft elevation and above. Below 5K feet, stock jets were used.

Mercury used to have jets for altitudes between Sea Level and 2500ft, 2500ft - 5000ft, and 5000ft - 7500ft
http://162.144.28.33/lib/mercury/manuals/mercury_1965-1989_2-40.html#/474

 

[hardwater fisherman]

Yes there is a small amount of tide in the area of the river where I go. When ice fishing you can see and hear the ice rising and lowering. Also you can see the rocks submerge along the shore. Did not think that would change much in the elevation.