Engine Timing Advance

[High Hopes]

Robert Hess < http://www.cncphotoalbum.com/atomic4/atomic4specs.htm identifies the timing spec of an A-4 as follows.

Adjustments Ignition timing Static:
No advance = 0° BTDC / Full advance = 17° BTDC

Dynamic:
<700 rpm = 0° BTDC / >1,800 rpm = 17° BTDC

Using this a a guide, I found that the engine will purr like a kitten when idling at 800 rpm. At 700 rpm, the distributor just starts to advance the spark. This gives a few degress of advance at 800 rpm. The engine idles well this way.

However, I am finding that althought the advance of the ignition timing proceeds nicely to about 17 degrees at 1800 rpm, at higher rpms, the timing advances even further. My A4 doesn't like this. The total advance is about 24 degrees at 3000 rpm.

Is there some adjustment on the distributor that limits the spark advance?

Steve Markowski

[Don Moyer]

Steve,

In 1995 we published an ignition advance curve in one of our Atomic 4 Newsletters (copy attached). This curve (developed by Tom Stevens of Indigo
Electronics) shows that the ignition advance continued to 21 degrees at 2000 RPM. Robert, Tom, and I were all in the practice of sharing information freely in those years so I'm not sure why Robert indicated that 17 degrees was a max advance in his data.

Of more relevance is the question of why your engine doesn't like the higher advance at high RPM. My guess is that you're evaluating your performance in neutral. For some reason (that I've never figured out) the Atomic 4 develops a slight "hiccup" at higher RPM in neutral. This anomaly is not present while the engine is under load. As long as your engine pulls smoothly under load up to its maximum RPM available, you should be OK.

Don

[High Hopes]

Wow Don. Thanks a lot. This is exactly what I was looking for. Yes, the engine is not under load (sitting in my garage). I can't wait to run her this am and set the timing again and get that smooooooooth idle sound again.

Best, Steve