Manual Ignition Timing Control

[old man emu]

I doubt if anyone here has had a daily drive that did not have some automated means of controlling the ignition timing in response to the operating speed of the engine. I believe the first type was the vacuum control, then centripetal weights and now it's all computer controlled. But what if your daily drive, or in my case, daily ride, was built before the introduction of these automated controls? How do you control the ignition timing? More importantly, how does someone who has never experienced the joys of using a manual spark control learn how to do so?

 

My bike's engine was was introduced in 1937. I suppose it's major advancement was the introduction of a pump to recirculate the engine oil, doing away with the previous "total loss" oiling system. However, automated spark control isn't a feature. Ignition timing is controlled via a twist-grip cable connected eventually to the points. Although twin cylinders, these engines do not have a distributor, just an engine operated "make or break" switch controlling the current through the primary wiring of the ignition coil. Whenever the timing cam opens the points, a spark is generated in both cylinders in what is known as a "wasted spark" system. By twisting the grip on the handlebar, the timing assembly can be rotated, altering the point at which the cam opens the points.

 

When I got the bike, I thought I already knew that the starting procedure required the timing to be moved to the fully retarded position, mainly said to avoid kick-back of the starter pedal into the lower leg muscles. But what after that? All I ever did was to return the timing to full advanced. Often I had trouble moving off. I had to rev the engine up high and when I engaged the clutch, I often stalled the engine. Interestingly, the operator's manual does say to start the engine at full advanced and to retard the spark slightly when the engine is laboring.

 

 Recently I was having a conversation with my bike's mechanic about the timing and he told me that I had to make more use of the spark control. That's OK, but what if you have never needed to understand why the timing of the spark has to change with the operation of the engine because everything you have driven or ridden has the operation done automatically? So I got researching the topic and from my findings I wrote a  short explanatory note. You might not be riding an old Flat Head, Knuckle or motoring in a T Model, but you might find what I have written entertaining if not educational.

 

 

 

 

Ignition Timing Control.pdf

[facthunter]

The fuel should be combusted BY tdc. This might seem ant -intuitive but that is a fact.. The KTOR JAP had to run 45 degrees of advance at revs because of the combustion chamber shape. Higher revs can take more advance.  Manual advance needs you to have a good feel of the motor  Something riders of modern bikes never have to have to the same extent. Retard position will make the engine run hotter. and produce less power.   Nev