Boat Engine & Pyramid Question

[Frank77]

After never having owned a boat before, I just purchased a 14' aluminum boat. I took it to Castaic to try it out and the 9.9 Johnson ran really well. In fact, I was very surprised at how fast this little engine is! I then took the boat to Pyramid the following week and it seemed the speed slowed considerably! I just couldn't get the boat "going" as it did at Castaic.

Will the elevation at Pyramid affect the speed of this engine that much? It just seemed very sluggish.

[cutbait]

Absolutely

The easy correction is to buy a lower pitch prop.

One for castaic, one for pyramid, problem solved

[Frank77]

I appreciate your reply cutbait. I'll do it!! Thanks!

[Bassnman Mike]

I have a friend that has an older Champion with a carbureted Mercury motor. While it runs great at Isabella if he goes down to Casitas or up to Crowley it runs like crap due to the elevation change. He takes the time to re-jet the carburetor however with my fuel injected motor, it does seem to run a little rougher, it seems to adjust as needed for the change in elevation.

Here's a good read.

http://blog.boattrader.com/2012/03/high-altitude-boating-where-did-the-power-go.html

[fishfinder]

i just carry a screwdriver with me and adjust the carb for the elevation. but going from castaic to pyramid shouldn't be that much difference. i just took mine to gull lake at 8500' and didnt need to adjust it at all. I never tried to go over 15mph but it seamed the same. now my last boat was a dog when i went to higher elevations. but i think adjusting the carb is pretty easy.

[cutbait]

While adjusting Carbs will certainly get the fuel mix to a correct state, the only real answer for slow speeds is a different prop.

Keep in mind for every 1000 ft. elevation you will lose 4% oxygen. I am not sure what Pyramid elevation is but I guess 5,000..

So 4% X 5 is 20% power loss at Pyramid. Congrats your 9.9 hp is now a 7.9 hp... whether you adjust the carb or not...

Keep in mind when you go to higher elevations, your mix will be running richer. {less oxygen in the mix with the elevation}.. If you adjust your jets to compensate and forget to or neglect to when you drop elevation you will then be running LEAN.....

In summation it is my opinion that no real power will be gained from adjusting the carb, only running smoother, but the danger of running a lean engine in the lower elevations will burn you up a piston if you neglect to adjust back.

Besides which, changing a prop in 1 minute is way easier than fiddling with that carb which doesn't give you anymore power anyway.

The prop will give you more bite, get you on plane, however you will lose top end speeds. and if not swapped at lower elevations will severely limit your top end speed

[Frank77]

Thanks once again for your input on this issue CutBait. I look forward to seeing you on the lake sometime.