It sounds like you have covered most things here, but do study the wire connection into the contact breaker points...if the points are open there should be no direct connection to earth. Also check that the points are actually opening to the correct gap of 15 thou - there is a peg operated by a cam which opens the points and this is prone to sticking. Go for a brand new plug too, or better still pull the plug cap back, and position the plug lead close to a metal part of the engine as you crank it over. Its best to look for a spark in the shade, rather than sunlight. I assume the flywheel key is intact?
John, May 2009
