carb adjustment for high altitude?

My 6 HP 4-stroke Merc outboard is about eight years old. I use it almost exclusively at an alpine lake (6,000 feet altitude) in the Sierras. Whenever I want to slow it down to a modest RPM rate for trolling or some other reason, the engine dies. It occurs to me that there might either be an adjustment on the carburetor for high altitude slow running, or a gas jet conversion kit.
Can anyone here suggest what I ought to do?

What is the serial number of the motor?

http://www.marineengine.com/parts/m...4stroke/0r000001-thru-0r067089-usa/carburetor
It looks like the pilot screw is the slow speed fuel mix needle you can try leaning it out rule of thumb for a two stroke is two jet sizes for every 2500 ft elevation.
Fuel jets are smaller the higher up and air jets are larger at higher altitudes. Call seaway marine in lynnwood WA they may have the proper info and jets. Just make sure and put the proper jets back in for running at lower altitudes or you will cook the valves and pistons.

kimcrwbr1 said:

What is the serial number of the motor?

Click to expand...

Sorry. The motor is at my cabin and I don't have a record of its s/n here. I'll be able to answer this is two weeks. But thank you for your response.
BTW: What info would you get by knowing the s/n?

Thanks for your response. I assume the jet sizes for two-stroke (as in your response) and four-stroke (which is what I have) are both changeable for high altitude. Correct?

you are correct,higher altitude = smaller jets+ thinner air

You need to give the model and serial number when calling a tech/parts person for the proper jet size for your altitude the high speed jet is on the bottom of the nozzle in the float bowl and the pilot jet is on top of the carb next to the idle air adjustment.
http://www.marineengine.com/parts/m...4stroke/0r000001-thru-0r067089-usa/carburetor
This just an example you need the serial number if you look at the part number you get the idea #4 is the pilot jet #5 is the slow needle and #7 is the high speed jet you may also need to change the nozzle size, Theoretically you will need to reduce the high jet six sizes? Right now your running too rich and probably carbon fouling the plug and valves. Once you confirm you have the proper jet sizes do a good decarb and then final the air adjustment.

If it does when you slow down, simply readjust the idle mixture screw and you should be okay.

Jeff

Related question... I found the high altitude jetting chart in my service manual for a '96 Mercury 125hp. It has suggested sizes for various altitudes. The motor is going from near sea level to 8800' where it will be used almost exclusively from now on. I know the carbs need smaller jets, and prop needs less pitch. I'm a bit confused on how to read this jet chart. It says factory jets are usually ok up to about 5000', but after that they should be reduced according to the chart. So the chart gives the factory jet size, and what it should be reduced to for every 1000' of elevation gain. My question is, is that chart for every 1000' above 5000', or every 1000' above sea level? If I read it the first way (every 1000' above 5000) then my jets would go down from the stock sizes .070,.080,.078,.082 to .068,.076,.074,.078. But if I read it the second way (every 1000' above sea level) then the jets would drop further to .064,.072,.070,.074. Which one is correct?