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Discussion Starter #1
When running a 2 stroke outboard in really cold temps, say down to 15 degrees.
Do you need to jet the carb richer? It would make sense that most outboards
would be jetted to run at temps around 60 or 70 degrees. A cold spring or fall
morning would be no problem. But temps down below freezing could cause the
motor to run too lean and burn up a piston. I know with 2 stroke snowmobiles this is a common problem. Has anyone had a problem with the jetting on their
outboard when running it in the winter?
 

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BUGBOAT,
This is a good question, since I don't have a snowmobile, I would like to ask something in regard to this.
Would it really matter with an outboard, figuring you have a thermostat and it is water cooled ? :confused:
Rich
 

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I have a 92-93 Evinrude that has run many,many hours and river mi. in temps as low as 10. Have yet to have any internal probs of any kind. How much difference would there be between an outboard and a snowmobile, or even a chainsaw running in these temps except for the water cooled part? Once warmed up they all run just fine.
 

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It really doesn't matter if a snomobile is liquid cooled or air cooled, the problem being that when it gets cold, the air/fuel mixture is effected. The colder it is, the leaner the mixture becomes, therefore, alot of guys runs really fat jets (larger) so when it does get cold, it doesn't burn up. Whether the engine is cold or hot, it's the temp of the air that it is sucking in that's the problem.

I've often wondered why outboards are not effected myself, but I've not heard of anyone having any problems. I don't know what kind of RPM's most outboards turn, but by running mine (25 hp. Merc) I have to think it's not as high as snomobiles (up to 9000.) I'm guessing that this is probably the contributing factor.
 

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Discussion Starter #5
Thanks alot Raymond. Thats kinda what I was thinking too. Many snowmobiles I believe are probably jetted "spot on" to get the most horsepower. So a little too cold a temp and your air fuel mixture gets too lean, and then a burnt piston. I didnt think I would have any problems, I just wanted to know If other people had experienced any difficulty.
 

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Thanks Raymond. That is strange that OBs don't seem to be effected by this. I do know that some chainsaws run even more RPMs then your example of the snow machine. :confused: Anyone else got any input on this? :grouphug:
 

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The deal with jetting is a gasoline will evaporate in 14.7 parts of air. This is the optimum fuel/air mixture. As the air cools there is more oxygen per cubic foot. The carbs can only take in so much air at a time. Same volume but more oxygen. Need more gas to compensate for the cold. Keep the gas output at the same level and it has too much oxygen and burns hot. 1280 aluminum melts.
There are usually more than one jet too. Main jets are for 3/4 to wide open. The needle that goes into the main will adjust for 1/4 to 3/4. The pilot jet is in effect from idle to 1/4 throttle.:confused:

Take a look at any chiltons book at the spark plugs in the back. This is the cheapest way to determine how they are running. If the plugs are black it is rich(too much gas). If it is white it is not getting enough. Should be a tan color.

Snomobiles are jetted to run at cold temps. Warm temps they get too much. Some racers lean the motor way way down. Running temps of 1300+. But it is just for a 6 second race. Anymore than that your buying a new motor. Outboards would run on the lean side in the cold but if your putting or trolling it should be fine.
 

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Wow!, you guys are much more knowledgeable on this subject then myself. Question....would it help to add an addtional ,say 10% more oil to the OB mixture then normal during extreme cold? As I said, I have never had a prob but don't want any either. :confused: Thank you for the great input on this.
 

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Id think that adding oil would only foul plugs out quicker. it would not reduce exhaust gas temps. I would just take it easy on it and you will be all right.

It only takes a few minutes to look at plug color.
White-bad, black-gonna foul a plug if putting. Tan-tear it up.
 
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