2005 Mercury 115 hp elevation ???

[MXDAD777]

I have a 2005 115hp outboard jet on my 18' Alumaweld. The motor has always ran flawless. I live at sea level and this is where I always use it. This past weekend I took it up in the mountains (5500' elevation) to do some lake fishing. The motor started right up and sounded fine, but my top speed was only 10 mph. Back home at sea level it easily runs 32 mph. The motor is EFI so it was my understanding that the elevation wouldn't effect it. Is that right? I had it out back home last week and it ran fine. Three days later at elevation it won't get my boat on plane. Any ideas? I want to go drop it in the local river to test it, but I can't do that until next weekend. It's killing me wondering what is going on. Thanks in advance for any input.

 

[sschefer]

Re: 2005 Mercury 115 hp elevation ???

When I head up to the mountains at 5100 feet I run 2" less pitch on my prop and I run a vented prop. Last year with my 100 on my 18' Legend I maxed out at about 30mph. I also run 89 octane fuel when I'm up that high. I only go up there once or twice a year so I don't bother re-jetting.

This year I'll be switching from a 1.87:1 to a 2:1 gear case and taking a couple of different props with me just to see how the act with my 150.

 

[MXDAD777]

Re: 2005 Mercury 115 hp elevation ???

I have a jet so prop pitch isn't the problem. I was running fuel from back home, but I don't think that would make that much of a difference. Some yes, 70% loss, no. Something isn't right, but thanks for the tips. Any other ideas???

 

[sschefer]

Re: 2005 Mercury 115 hp elevation ???

I have a jet so prop pitch isn't the problem. I was running fuel from back home, but I don't think that would make that much of a difference. Some yes, 70% loss, no. Something isn't right, but thanks for the tips. Any other ideas???

There's always someone in the parking lot at the ramp cussing their motor up at Eagle Lake, Ca. 5100ft. The story is the same as yours so it's not an uncommon one. Why some motors react the way yours does and others don't is a mystery to me. I know my old 4 stroke Nissan 18 would loose about 1/3 power up there.

 

[MXDAD777]

Re: 2005 Mercury 115 hp elevation ???

There's always someone in the parking lot at the ramp cussing their motor up at Eagle Lake, Ca. 5100ft. The story is the same as yours so it's not an uncommon one. Why some motors react the way yours does and others don't is a mystery to me. I know my old 4 stroke Nissan 18 would loose about 1/3 power up there.

I was afraid that might be the case. I'm going to try and sneak out to the local river after work today and see what it does. If it runs fine (which I have a feeling it will) I guess I am just stuck with a great valley river boat and a lousy high elevation boat. Anybody else have any experience along this line?

 

[fishrdan]

Re: 2005 Mercury 115 hp elevation ???

HP loss at elevation is about 3% for every 1000', so you are loosing about 15%. For prop boats it's normal to drop prop pitch at elevation so the engine will spin up into the power band easier. Not sure if they make lower pitch impellers for your jet pump, but I imagine it would be a real pain to swap if possible.

I'd almost bet a week's pay check that your engine is going to run just fine back at sea level , it's the elevation that's killing performance,,, been there, done that.

Here's things that can help high altitude performance;
- reduce weight from boat, all extra's get left at the dock
- reduce prop (impeller) pitch, not easy on your rig I'd think
- rejet carbs leaner, (EFI handling it?)
- bump timing, I wouldn't do it without experience, which I don't have, so I can't recommend

I was running at 5000' a couple weeks ago with my Mercruiser 140HP and the boat was a bit sluggish, but still was able to get on plane with a load of people. That was after jetting down the carb and dropping to a 17P prop. If I had the boat with it's sea level setup it would have been a pig.

 

[MXDAD777]

Re: 2005 Mercury 115 hp elevation ???

I just got back from the river and all is well. The boat took right off and jumped up on plane and cruised at 34 mph. It ran flawless as usual. I left EVERYTHING in the boat that I had at Stampede and also had 3 people in the boat, just like at Stampede. I wanted to keep all the variables constant. Anyway, I love my boat and it works like a dream at 90% of the places I fish. I'll just have to put up with it when I go to Stampede or any other high elevation lake. Good thing it's a small lake.
Thanks for the ideas and input.

 

[sschefer]

Re: 2005 Mercury 115 hp elevation ???

Come on over to Eagle and we'll go fishing. New moon is on the 12th, I'll be there until the 19th. I'm taking the 18' with the 135. Lake is low. Don't want to suck up a ton of silt and rocks with the North River. Sux, I was hoping to show it off!

 

[MXDAD777]

Re: 2005 Mercury 115 hp elevation ???

Come on over to Eagle and we'll go fishing. New moon is on the 12th, I'll be there until the 19th. I'm taking the 18' with the 135. Lake is low. Don't want to suck up a ton of silt and rocks with the North River. Sux, I was hoping to show it off!

I just might do that. I haven't fished Eagle Lake in over 15 years. If memory serves me right, there are some real monsters in there.

 

[sschefer]

Re: 2005 Mercury 115 hp elevation ???

I just might do that. I haven't fished Eagle Lake in over 15 years. If memory serves me right, there are some real monsters in there.

The fish aren't what they were 25 years ago but if you know where to fish you can still find a monster or two. PM me if you want and I'll give you more info.

 

[MXDAD777]

Re: 2005 Mercury 115 hp elevation ???

The fish aren't what they were 25 years ago but if you know where to fish you can still find a monster or two. PM me if you want and I'll give you more info.

PM sent

 

[sschefer]

Re: 2005 Mercury 115 hp elevation ???

PM sent

Got it and responded.