Yahama Air Cooled Engine

[Alwyn]

I have a Temperamental outboard engine - Yamaha 5BS Air Cooled Engine NO:661S - 02174,Sparking Plug B9HS10,is this the right Plug For the Engine?
What is the correct mixture for this engine?
Engine starts first time on water - Once stopped will not start again. No problem on dry land will start every time. Any ideas what could be wrong with the engine? /forums/images/graemlins/confused.gif

 

[bdsweeting]

Starts first time but not afterwards ??? Is the exhaust outlet too deep in the water (due to everyone looking over the transom at it !) causing high back pressure ?