Ignition timing

Data is correct, but sounds as if the timing is way off. Also check the careburettor for blocked jets, dropped needle etc.

Hi Mark,

Yes the data is correct but there may be some other point you may have missed, but I apologise if you have checked the following already.The first thing to check is the chain tension which should have 1/4" up and down movement at the mid-way point. A chain that is too tight can sap engine power although yours seems too much to be just that. The next thing to check is wether you have a tight or slack wire advance. On the 1938 engine the mag runs clockwise when viewed from the chain side so for the preferred slack wire the advance and retard cable should exit the mag on the side nearest the oil tank, so if it's on the engine side it's tight. The points should have a maximum gap of 12 thou. and the timing point is 5/8" or 45 degrees before TDC on the 490cc engine, at which the points should just be opening i.e 2 thou or a fag paper if you prefer. This is at full advance so check where the handlebar lever should be, tight or slack. A good check is to run the engine up to temperature and set the tick-over a little on the fast side. The engine should run fully advanced and fully retarded with-out any tendancy to stall or faulter. This may take several goes to get the timing right. as the 5/8" setting is only an approximate setting as modern fuel might need a different setting to the petrol used 77 years ago. Hope this helps, Richard.