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1999 2.5 hp Mercury at 67000 feet

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I have an old 2.5 hp I just cleaned out the carb and go running. It pushed my tiny sailboat across the lake just fine but being at 6000 feet, I was wondering if I should try to adjust the carb or exchange the high speed jet for one that is better for high altitude?
 
Did you buy the engine locally? Does it run well? It would run rich if it had low altitude jets and an old engine from the area should have been jetted properly already. Run down a shop manual, it should have the recommend jet sizes listed to check against.
 
Nothing to it, on Mars. There's a mountain there that's 90,000 feet high--three TIMES the height of Everest!

Jeff
 
Typo, the boat is at 6700 feet. I am taking it to 2000 feet next week.

I bought it in Utah at 4000 feet, had it run in San Diego at sea level. It does run okay at 6700 feet but does not idle so well. For what i am using it for I would like to have a few different jets to change it up to get the max from it at a given altitude.

I may be upgrading from the boat it is pushing so don't want to invest in a manual just yet.
 
Looking at the manual for my engine it says that from sea level to 2500 use standard jets, from 2500 to 5000 go .002 smaller and from 5000 to 7500 go .002 smaller than that soknowing what is std for yours would be needed. The manuals cover a number of engines so it might not be a waste at $15 or so. I just thought of something, the jet sizes are listed in the carburetor breakdown in the parts lookup, you could go there. Be aware that there could be a serial number range difference in sizes (probably sizeable) if so find those in similar range to what is in your carbs.
 
Remember that your engine is likely jetted for 4000 ft and will be .002 smaller than std or sea level size and for your area you will need .004 smaller. On my engine (a 140 hp) there are three jets that have to be changed in each carb so look carefully at the jet listings.
 
Swagonmaster said:
Remember that your engine is likely jetted for 4000 ft and will be .002 smaller than std or sea level size.
Click to expand...

I am not sure of that. We bought the boat for $1000 with the motor and a battery and electric trolling motor. The previous owner loved the boat but did not know what he was doing. With what I found on other parts of the boat, don't know the motor was upgraded or not.

The problem I am having is most charts I have found start at 4 hp. Tomorrow I will pull the motor's cowling and hope to be able to find a SN and track down the jet options.
 
So I swapped out the spark plug for a new one. The gap was sized correctly according to the specs inside the cowling. It was harder to start than normal and would die after a few minutes. It would start up and run a few minutes then die again.

What else can I try to get this running smoothly. I can not find a way to upgrade the jet as there is no chart for motors this small.
 
Without your engine serial no i can't give you numbers but when I looked up a random 1999 2.5 in the parts listings here in the carburetor section they list the jet sizes with standard being sea level and the optional jets being higher altitudes.
 
Sorry about that, just found the serial number is a hidden place. It is fairly impressive the amount of info the Mercury includes inside the cowling. The serial number is under the motor and only available when the motor it tipped up.


s.n. 0G713802
 
That's interesting, no optional jets are listed for your engine. They identified the jet as a #86 so I guess it would be possible to find another jet but I'm not sure it would be worth the trouble. My advice would be to just run it since it seems to be doing ok.
 
Any more power loss on a 2.5 and your back to rowing? See if it runs any better with the cowling off......just for fun! I have an oxygen concentrator for sale too. Use it every now and then to make sure it works.....trouble is you need to bring your Honda 1000 generator along too......then your gonna need a 3 hp for all the extra weight.
 
This is not a power loss situation. It is an intermittent running situ. My portabote weighs less than 100 lbs and my sailboat weighs less than 500 lbs. 2.5 hp is okay for both as long as it can stay running.

If the difference is a high altitude jet would give me more power, while good is not so important. I just want to have the motor run reliably in case the wind it too strong for the power boat or no wind for the sailboat.

Initially I had cleaned the jets to get the motor to run. It was hard to start but ran fairly consistently. Now it runs rough and dies after a short run time. I will try a deeper carb clean.
 
Just want to report back. I took this carb out completely this time. My previous attempt to clean was just as far as the bowl and jet that was easily reachable. I dismanteld and cleaned everything. It now starts with one pull and runs flawlessly on the stand at least. Lets hope it performs like that in the water also.

When reassembling I found an o-ring in the bottom cowling. It fit in the area that went between the carb and the motor. Not a snug or custom fit, just sat inside the carb's union with the motor. It is the only place i can think of where it might have fallen out of. But it could also have just been floating in the cowling from somewhere else from another time. I put in into place and pushed the carb back into place but the carb does not seem to go on as deep as it should leaving the plastic plate a bit proud of lining up with the cowling.

I am trying to add a photo but the forum is not allowing me or at least I go through the steps and no photo appears.
 
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