I have now had the magneto professionally refurbished. It has been fitted with a new condenser and coil. The original condenser was found to be completely shot and the coil was way past its best. According to the test results following the rebuild, the minimum rotor speed that the mag needs to produce a consistent spark when cold is 138rpm (so 276rpm engine speed). After heating to 50 degrees celsius, the rotor speed needs to be a minimum of 170rpm. The spark remained consistent all the way up to 3000rpm.
So, I fitted the mag back to the Norton and after 20 minutes of pulling on the starting strap, it did eventually fire, once!!! Not to be detered, I continued pulling for another 10 minutes before it sputtered into life, albeit for only 5 seconds, but I’ll take that as a victory!!!!
I have set the timing so that the points begin to open at exactly top dead centre, as I believe this is normal practice to make starting easier (allegedly!!!). Would I be right in thinking that the quoted figure of 3/8″ before TDC relates to once the engine is running normally and that this is achieved by adjusting the lag angle. According to the Norton engine manual 3/8″ equates to 28 degrees, so is this what the lag angle should be set to?
Now I am confident that the mag is working as it should, I think the carb needs some adjustment. The carb is an Amal 225. I have read previously on this forum that the main jet needle should be wound in until fully seated and then wound out by one and a half turns, which I have done. There is also an air adjusting screw fitted at the air intake end of the carb, running parallel with the body. Does anyone know what position this should be set in?
Finally, I was testing the engine without the air cleaner connected up, so could this cause the engine to get too much air and make it difficult to start?
As usual, any advice on the fine art of magneto setting and carburetion would be greatly appreciated.
Cheers,
Sean
