When you take out your spark plugs, if the colour of the electrode is metallic grey, and the electrodes are grainy or stuck fast, the causes may be: The ignition is too early because the insulation is too hot – you may have the wrong spark plugs. If this is the case the power will decrease sharply. Get the engine checked in a workshop before you use it again.

(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)