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Blowing white smoke and lumpy idle 2015 Sherco 300ST

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I have recently replaced cylinder head seals and the bike is still blowing white smoke - more as it heats up. The idle is also surgy/lumpy and irregular with a throttle over run...are these things connected? What else could be causing the white smoke?

Thanks!

Rule of thumb is white smoke is produced by burning coolant.

Assuming the head gasket is leaking into the water jacket, typically that would force coolant out of the cooling system because combustion pressures are so much higher than coolant system pressure, it would be unusual for coolant to be forced or drawn into the combustion chamber during operation and more likely to leak coolant into the combustion chamber when it is not running.  Raw coolant might collect in the exhaust system and that will not steam or evaporate until your exhaust temperatures are very high.  I think you are looking for signs of coolant disappearing.  Anti-freeze has a distinct odour and that should be another tell.   

  • Author

Thank you lemur, I have already changed the cylinder head seals (twice)...still blowing white smoke and coolant level going down - cracked cylinder or cylinder base gasket?

 

 

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