JIMTMCDANIELS
Member
Hi I'm just paying this info forward and sharing here what I couldn't find in a manual or online about resetting rejetting for high altitude:
A copy of a bulletin someone e-mailed me(the 4 pages they sent-they said are the only pages needed with the details) for the recommended changing the carb orifices on my 2 cycle Outboard Motor for High altitude use(over 3,000 feet)(under 3,000 feet-no modification is needed).
I live here in CO at 6,000 feet. Others may find this helpful.
OMC Evinrude/Johnson Outboard Carbs Fuel Jets orifice size High Altitude modification Jan 1990 Service Bulletin including exact chart for 85, 90, 100, 115, 140, 150, 175, 200, 235 motors.
This bulletin also gives some sea level orifice sizing and a general description of high altitude orifice selection and a brief description of prop changes for High Altitude.
Note: On the chart, some of the orifice size/hole recommended actually increases(instead of decreases) as the altitude increases because those orifice system circuit designs actually have air passing through the orifice instead of fuel.
So at higher altitude the air is thinner/less oxygen so less fuel(smaller orifice if it controls/passes fuel flow) is needed to maintain the proper air/fuel burn ratio or more air is needed(larger orifice if it controls/passes air flow in that carb circuit design).
i.e. some of the low speed orifice sizes actually increase as the altitude increases in the chart because air passes through that orifice, not fuel but the high speed orifice circuit decreases in size selection.
Note:
This bulletin is before 10% Ethanol was introduced into our gas and if you are using 10% Ethanol gasoline, I don't know if it effects what is recommended for orifices but I don't think so.
Note:
There is danger of burning up the motor/pistons causing major damage if it is run too lean by making the wrong orifice selection to an extreme.
Note:
Even though I bought my used 1984 Evinrude and boat from a local seller and found papers showing the boat sold years ago(possibly when new) in CO, it still had the sea level sized orifices installed.
Note:
Using sea level sized orifices above 3,000 feet, instead of making a high altitude change, increases fuel consumption and increases the exhaust odor of unburned gasoline(no fun if your being towed behind the recreational boat having to smell it), can cause reduced running quality of the motor and I would say pollutes the lake water more....
Note:
If you do change the orifices for higher altitude, of course you'll want to clearly record in maintenance records and label the motor so that any future owners will know not to operate at lower altitudes without changing the orifices back, otherwise a lean condition that overheats the pistons causing major damage could occure.
I had to do some googling to determine which version of 140 engine was mine in the chart based on the serial number.
I found the cheapest price for new or used orifices on e-bay.
Note the 4 different orifice types, some look a lot a like do don't buy the wrong ones.
To removing/installing the orifice, use a quality small screw driver that the blade is as wide as possible without scraping the threaded wall of the orifice hole.
A poor quality screw driver tips may just bend as many small screw drivers are poor quality.
The orifices can be tight and make a bit of a snapping sound when first breaking free as you turn counter clock-wise.
When installing the orfices, do not over tighten as they and the threads are small and soft metals, they just have to be snug is all.
I'm glad I made the change as exhaust is less stinky but still stinky to ride behind. I haven't used the boat too much so I can't give description of the performance before and after the change.
I will never push my luck and take my boat more than 100 miles from home in fact I only go to 2 lakes and both are about 50 miles away north or south of me. There are lakes west up in the mountains but I don't want to wear my vehicle pulling up hill and they are mainly cold fishing spots up there and I don't fish.
That's all the info I can think of on this that I've learned.
Take care
Jim
A copy of a bulletin someone e-mailed me(the 4 pages they sent-they said are the only pages needed with the details) for the recommended changing the carb orifices on my 2 cycle Outboard Motor for High altitude use(over 3,000 feet)(under 3,000 feet-no modification is needed).
I live here in CO at 6,000 feet. Others may find this helpful.
OMC Evinrude/Johnson Outboard Carbs Fuel Jets orifice size High Altitude modification Jan 1990 Service Bulletin including exact chart for 85, 90, 100, 115, 140, 150, 175, 200, 235 motors.
This bulletin also gives some sea level orifice sizing and a general description of high altitude orifice selection and a brief description of prop changes for High Altitude.
Note: On the chart, some of the orifice size/hole recommended actually increases(instead of decreases) as the altitude increases because those orifice system circuit designs actually have air passing through the orifice instead of fuel.
So at higher altitude the air is thinner/less oxygen so less fuel(smaller orifice if it controls/passes fuel flow) is needed to maintain the proper air/fuel burn ratio or more air is needed(larger orifice if it controls/passes air flow in that carb circuit design).
i.e. some of the low speed orifice sizes actually increase as the altitude increases in the chart because air passes through that orifice, not fuel but the high speed orifice circuit decreases in size selection.
Note:
This bulletin is before 10% Ethanol was introduced into our gas and if you are using 10% Ethanol gasoline, I don't know if it effects what is recommended for orifices but I don't think so.
Note:
There is danger of burning up the motor/pistons causing major damage if it is run too lean by making the wrong orifice selection to an extreme.
Note:
Even though I bought my used 1984 Evinrude and boat from a local seller and found papers showing the boat sold years ago(possibly when new) in CO, it still had the sea level sized orifices installed.
Note:
Using sea level sized orifices above 3,000 feet, instead of making a high altitude change, increases fuel consumption and increases the exhaust odor of unburned gasoline(no fun if your being towed behind the recreational boat having to smell it), can cause reduced running quality of the motor and I would say pollutes the lake water more....
Note:
If you do change the orifices for higher altitude, of course you'll want to clearly record in maintenance records and label the motor so that any future owners will know not to operate at lower altitudes without changing the orifices back, otherwise a lean condition that overheats the pistons causing major damage could occure.
I had to do some googling to determine which version of 140 engine was mine in the chart based on the serial number.
I found the cheapest price for new or used orifices on e-bay.
Note the 4 different orifice types, some look a lot a like do don't buy the wrong ones.
To removing/installing the orifice, use a quality small screw driver that the blade is as wide as possible without scraping the threaded wall of the orifice hole.
A poor quality screw driver tips may just bend as many small screw drivers are poor quality.
The orifices can be tight and make a bit of a snapping sound when first breaking free as you turn counter clock-wise.
When installing the orfices, do not over tighten as they and the threads are small and soft metals, they just have to be snug is all.
I'm glad I made the change as exhaust is less stinky but still stinky to ride behind. I haven't used the boat too much so I can't give description of the performance before and after the change.
I will never push my luck and take my boat more than 100 miles from home in fact I only go to 2 lakes and both are about 50 miles away north or south of me. There are lakes west up in the mountains but I don't want to wear my vehicle pulling up hill and they are mainly cold fishing spots up there and I don't fish.
That's all the info I can think of on this that I've learned.
Take care
Jim
