That BTH advance unit I modified on that Velocette I had here a few years back was going to full advance way too soon........came very close to damaging his engine.........Probably getting to full advance by 2000 rpm or less........Not good.
Interesting, as I suspected fully retarded to fully advanced within 500 rpm difference, hardly a controlled advance curve, but don't forget this was early days of auto advance and the only other option was a manual adjust lever on the handlebars and this basic ATD did its function on thousands of bikes across multiple manufacturers. You cannot compare it against electronic controlled advance which came along 30 plus years later.Interesting paper from BrightSpark magnetos regarding ATD performance
Hi Simon,Vic
I woudn't say that Lucas was stuck in pre war thinking, it was probably more that Lucas didn't want to spend any money to make a better product. I remember reading once it was BSA that told Lucas they wanted to pay no more than X and so Lucas made them to that cost and the rest of the industry had to suffer the consequence as BSA was their largest customer.
When you look at the size of the weights in a car mechanical distributor generally they are a lot smaller and weigh less and so easier to control by springs etc. I suspect that is what is wrong with the Lucas magneto ATD and Martyn may be onto something reducing their size.