4 stroke carberation and elevation problems?

[keninaz]

I want to buy a lake boat and here in AZ that means less than 10 HP and a 12-14' aluminum boat for me.
The last outboard that I owned was in the early 1980s so I am certainly not up to date on information.
I see that all motors now are 4 stroke and the 10 HP range are all carbureted that I see.
So that takes me back to the days when cars had to have jets changed to perform better at elevation.
I would like to fish the lakes of AZ and they vary greatly from around 2000-7000'. I know I will lose power at elevation and that cannot be helped. But I was wondering about performance at idle and such for low speeds and how well the newer motors work.
Or is there an adjustment to allow owners to make while using the motor at elevation?

 

[Frank Acampora]

Just as if an older car was going to be used at elevation for any length of time, the jets must be resized to accommodate the less air and oxygen the engine can pump. The high speed jet limits fuel flow at full throttle and should not affect idle. Up to 2000 feet, you can probably get away with the original jets. Over 2000 you most likely need to jet leaner. Best advice for sizing would come from a dealer/repair shop.

 

[keninaz]

OK, TNX. I expected I could have a problem with the wide elevations I want to fish at.

 

[Sea Rider]

For high elevation boating better contact engine manufacturer, some of them as Merc have elevation jet kits in steps of 1K meter elevations. If you will be boating at such different altitudes between lakes will have a performance problem with an engine jetted for way less altitude and then going to a higher altitude with same jets.

Better pick different lakes which are about same altitude and re jet engine for those, a less pitch prop will also be needed for best engine performance, not top though as when boating at sea level but much better than doing nothing. An engine can lose as much as 15% of its HP every 1 K meter of elevation. Engine will benefit running low octane fuels at high elevations too.

Happy Boating

 

[keninaz]

Yes it appears it's either that or forget the smaller lakes and go with computer controlled Fuel Injection like the newer cars have. It appears there is no simple solution.

 

[Sea Rider]

I have a electronic inyected car but when going at just 10 K feet of elevation feels like a slow pig, you wonder where did the nice power went. The issue is that at high elevation there's much less oxigen compared to sea level. Combustion turns weak. The higher you go the worst it gets, so really there's not much you can do running electronic inyected OB's at very high altitude and expect peak performance.

The only real difference compared to a carbed OB, is that the engine electronically adjusts itself to perform opt but lacking more proportional oxygen rate to compensate that altitude, just remains in good intentions, still will need a less prop pitch and low octane fuel to compensate a bit. Diessel engines performs much better at high elevations than carbed/inyected engines.

Happy Boating

 

[MTboatguy]

All of the boating I do is over 4000 feet and idle can be a real problem, if you are going to consistently be over a certain elevation, I would recommend finding a good middle of the road for changing your jetting, I know I have had to change mine to a good compromise in order to play in the mountains. Of course I live at 4500 so have had to change things in my older cars and trucks as well.