Very useful information on jetting and also on fuel consumption. Many thanks. This is the engine Ian Parsons built some years ago for sprinting with a sporty 500 cc cylinder block which (once had) chrome-plated bores and also oil feeds (Clubman’s Special or what? There are various odd numbers stamped on it)). It is mounted on a 600cc DPY bottom end so how the timing works out is a bit mysterious to me but it is extremely vivid and I don’t really expect fuel economy. I have ‘been there’ with the piston seizure problem and have set it up extremely carefully with an expert cylinder honer and borer using advice on the clearance at each point up the piston from the best experts!