Post by Dave Plowman (News) Post by Indy Jess John Post by Dave Plowman (News)
Think what happens is the rotor is centrifugal and moves to the point
where it is no longer pointing at the correct cylinder. But is a
pretty crude device causing a misfire. Not something you'd want to use
as a sort of cruise control. Because on a carb engine fuel is still
being drawn in, when it sparks again you can get a backfire.
I am pretty sure that mine was centrifugal but I don't think it pointed
to the wrong cylinder, it shorted the coil input to the rotating spindle
and therefore prevented the spark. I can't prove it now though.
Yes- that would work too. I can't say I've ever seen one. It does seem a
crude device to make reasonably accurate, though. Did it have some form of
over centre so it went quickly from 'go' to 'stop'?
I do remember it not being subtle on the Lotus Cortina I had a drive of.
On one side was the usual hook shaped wiper that carried the spark to
the spark plug terminals. Opposite was a weight inside a shroud that
was spring loaded and centrifugal force on that weight shut off the
spark. The weight had three tapped holes and a small bolt that went
into any of them. By having the bolt at adjustable distances from the
centre it was possible to set different rev limits for the cut-off.
When I bought the car, it was in the middle hole, and I discovered the
rev limiter effect during the 200 mile journey driving from where I
bought the car to my home. I didn't try the faster and slower settings
afterwards because the concept of limiting the engine speed in the lower
gears made no sense at all, and I just changed it for a standard rotor arm.
 I could feel the spring and it was quite a strong one, but I never
checked whether it was an over-centre arrangement.