INDIOMIKE, (and everyone):

The "Positive Stop" method eliminates that "rock" at top dead center that you speak of in your post. That rock can be several degrees and if not accounted for can throw your timing setting off enough to make a difference.

The Positive Stop method splits that "rock" precisely in half and when you set up your degree wheel using that method, you can be assured that when the degree wheel indicates zero, you are truly at top dead center. Using other methods, you will more likely than not be off on your settings. This is not some obscure method invented for model engines by some amateur. It is a tried and true method used by engine builders of ALL types of engines, especially race engine builders, all over the world for precise checking and setting of valve timing events, ignition settings, etc., etc.

Further, while your method of just looking at the magnet/sensor positioning may work as a very general, "down and dirty" field check of the timing to see if the timing has slipped, it should never be used to initially set the timing. There are just too many variables with that method, such as magnet strength, magnet to sensor gap, sensor specific characteristics, magnet diameter, etc., etc. to just rely on a visual aspect of the sensor/magnet locational relation to set the timing. You need to know when the spark ACTUALLY occurs, and where TDC REALLY is to properly set the timing. It only takes a few minutes to do it correctly.

The difference between a great running engine that is a pleasure to use, and a "so so" engine or a "dog" is in the details.

AV8TOR