Member Removed Posted November 12, 2007 Report Share Posted November 12, 2007 I Have a Yamaha 50hp 2stroke Outboard (fairly old) on my 18' boat. It has developed a problem whereby it lacks power. It appears to only be firing on two out of the three cylinders. Occasionally the third cylinder kicks in and there is a sudden surge in power but this only lasts a few seconds. Seems like the third cylinder ist trying to go but cant. Is this an electrical problem? is it something simple or will I have to get an expert in to sort it? Any iadeas?????? Steve Potter Quote Link to comment Share on other sites More sharing options...
great white Posted November 12, 2007 Report Share Posted November 12, 2007 Steve what have you done so far? If its nothing start with the simple inexpensive things Check that all the plugs are sparking OK they should be giving a strong spark and check that the leads are on correctly [Take care as they are very high voltage] If they are not change all the plugs If that does not sort it then it may be time to check and clean the carbs, as it could be a sticky float valve. or a blocked jet Charlie Quote Link to comment Share on other sites More sharing options...
britboard Posted November 12, 2007 Report Share Posted November 12, 2007 Run the engine and take out the plugs, they should all be a light brown colour if you find that one is oily or wet then that plug, ignition circuit etc is likely the problem. Whilst you have the plugs out do a compression test if you go to an auto spares shop they should be able to supply you with one for around Quote Link to comment Share on other sites More sharing options...
Rob Posted November 12, 2007 Report Share Posted November 12, 2007 You could have a head gasket leak in to the dodgy cylinder, however I wouldn't expect it to fire occasionally. As the guys have suggested, you need fuel air and spark. Spark is easy to check, air check your intake, fuel - not so easy to check but a fuel soaked plug would suggest that is ok. If the unit is auto mix it could be too much oil. Rob Quote Link to comment Share on other sites More sharing options...
Member Removed Posted November 12, 2007 Author Report Share Posted November 12, 2007 Thanks for the tips. Ive checked plugs, tested spark and condition of the leads. The carb suggestion sounds good so I'll have a go at it and also the compression test. Again, Many thanks Quote Link to comment Share on other sites More sharing options...
great white Posted November 13, 2007 Report Share Posted November 13, 2007 If you are cleaning the carbs and taking out the adjustable screws the trick is to gently wind them closed from the existing settings and note how many quarter turns that is, before removing them all teh way out. after cleaning you can reverse this process to return to the original settings and you should be sure to have a running engine hope that helps Charlie Quote Link to comment Share on other sites More sharing options...
Member Removed Posted November 13, 2007 Author Report Share Posted November 13, 2007 Thanks Charlie. Ill try that. Quote Link to comment Share on other sites More sharing options...
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