When you take out your spark plugs, if the colour of the electrode is dark brown, chances are the ignition is too early, there is not enough cooling water in the system (maybe the impellor is broken), there is air or a poor mix in the carburettor, the piston rings are stuck – take your engine to a workshop. There may be some blistering of the electrode.

(Taken from the Skipper’s Outboard Motor Guide, a brand-new fantastic waterproof handbook by Hans Donat, published by Adlard Coles Nautical, ISBN 978-1-4081-1418-6 – £10.99, and available from all good nautical bookshops)