Re: How do Atom Computer Ignition modules work?

[legendre]

I had a chance to run the engine this evening, and take some measurements. The results are pretty surprising.

Setting up:

Determining precise TDC on my test motor is difficult. Due to the plug hole being offset from the piston crown, there is no straightforward way to determine TDC using either a piston stop or a dial gauge. I had to eyeball piston height through the plug hole – made several observations and took the average of them.. but I think I’m within +/- 3′. Made a datum mark on the case with a file, and a TDC mark on the flywheel with a Sharpie pen.

Likewise, determining the fire point was a problem. All I could do was to set the points per the manual at 0.020" as carefully as possible, and then mark the ‘fire’ point on the flywheel with a sharpie using a beep-box to determine when the points broke open.

Measuring:

Started the motor, and used a strobe timing light to view the timing angle. Oddly enough, at idle and any low-ish RPM, the motor (running off the module, now) was firing +nearly spot-on+ with the ‘fire’ mark I’d previously made. That’s just got to be a coincidence, I’d think. But I repeated the start-up & measurement four times, and each time, the dang thing is hitting within +/-2′ of the ‘fire’ mark. So it is!

But here’s what’s more interesting. As the RPM is increased, the timing +retards+, rather than advances.. as one would expect. The retard isn’t highly significant, maybe 5-7′ tops, at full throttle. But it does leave a number of questions – such as, why doesn’t it +advance+ with speed, as one would expect from any other ignition system?

Crazy stuff! Any ideas, gents??