<VV> Got a Question- loss of power

[cmot at ix.netcom.com]

I used to see weird problems all the time, a good oscilloscope would show
the problem quickly. Lacking that and going by your description, and I
assume you are using points, you should check the following. The fact that
it takes time or heat buildup and was significantly cured by a high output
coil is the clue. I had in years past seen  lower quality point sets
actually have the point arm start to bind on it's pivot post at high speed
or heat condition. Sometimes a tiny drop of oil on the pivot cured the
problem and confirmed it. If the points are binding you could watch the
dwell period/cam angle start to drop on a meter as the points start to stick
open longer. Do not confuse this with the normal dwell change as the point
plate advances/retards with distributor vacuum changes. The point plate does
not pivot around the shaft but from it's own offset spring loaded pin which
causes point gap to change as it pivots and is designed to provide a dwell
change. As the points stick open the dwell lowers (small number = large
point gap) indicated by less point closed time the coil has less time to
saturate and the spark weakens. Your high output coil could be correcting
the problem by concealing it with higher output. 
	I had seen similar problems on early electronic ignition systems, a
defective ignition control module that would break down under 10 minutes of
high speed only (such as turnpike driving). I had also seen high output
coils that overheated when used with electronic ignition modules which they
were not designed for, they would leak out their insulating oil when
overheated and short out internally, initially only under high load or heat.
High output coils also have a higher current draw which fried some
electronic modules in time. This is why your see epoxy coils now in modern
electronic ignitions. Performance problems that initiated tune-ups were
usually point problems 9 out of 10 times. There are other things that can
cause problems such as deteriorated plugs or plug wires. Excessive rotor to
cap gap, occasionally seen in mismatched cheap brands. Bad distributor
ground or high points circuit resistance. But those problems are usually
constant by their nature, not intermittent. Actually improper heat range
plugs can cause a similar problem too. Years ago Champion consolidated heat
ranges and inventory. They came out with copper core plugs that they claimed
would cover a wider heat range. In reality the consolidated numbers were
usually a higher heat range and were fine around town on short trips. On the
road they overheated and damaged the resistor core causing a crack in the
internal carbon resistor. This would start to arc and burn out, effectively
increasing the plug gap and causing hesitation, stalling and lack of power
on a otherwise normal appearing "new" plug. Only a oscilloscope would show
the ruined plugs problem that could occur after one turnpike trip. In other
words, cross reference charts lie.
	It is difficult to accurately diagnose your problem here as visual
inspection is critical. I could give you things to look for in scope
patterns if you have one available.
Good luck
Chet Motyka


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