Runaway James
“How do you officially stop a James?” asks Adrian Player. No, it’s not a joke; his neighbour has just finished building a 1962 Flying Cadet and, since Adrian owns a 1939 AJS 250, thought he’d be the man to ask. “I had a look at it, but there’s no ignition switch, kill button or anything in the wiring diagram – and come to think of it, the same applies to my AJS... I hope it’s not a stupid question!” says Adrian. It’s a good point and, as usual, there’s a bit of a story to it. Magneto ignition is self-generating, so there’s no battery to switch into circuit. With no battery to drain, you can simply earth the low-tension circuit or the contact points to cut the spark. This is often done with a button on parallel twins while Villiers 1H and 2, 3 and 4T engines have an impressive-looking key switch on the crankcase – again, it just shorts the points to earth. But on single-cylinder bikes, like the AJS, there’s a valve lifter lever instead which lets out the cylinder compression, aiding starting and cutting the motor – well, unless it’s stuck revving its head off when it can develop enough compression to carry on going mental – a cut out is no bad thing. Two-strokes also perform best at high revs and these piston-ported designs were poor idlers on the pilot jet alone, the throttle needing to be set slightly open. So, while up until the mid-’50s most two strokes had decompressors, I suspect it was figured out that just fully shutting the throttle would kill the engine, saving the cost of any other fitting.