Gary---My reply here as to the issue of ignition timing at idle falls
close to Terry's corner. This is my understanding:
Triumph, in their effort to comply with our Feds knew that certain
emissions, namely NOx, was lower when the timing was "set back" at idle,
plus when the engine was on "overrun". They later had to do something
about the engine overheating at idle when the timing was retarded, so
they wisely incorporated a thermal switch into the vacuum line to the
distributor. This thermal switch only comes into play when the coolant
exceeded a given temperature. (Somewhere just short of boiling the
coolant, I would imagine) Mine cut in when the needle got to the 3/4
mark on the gauge, and the engine idle would speed up from 800 to 1300
rpm, and the temp would drop within a couple of minutes.
Anyway, with the thermal switch interrupting the vacuum retard, two
things happen. The engine speeds up due to the advancing of the ignition
timing. This promotes better cooling because of a corresponding speedup
of the water pump and fan, plus better engine efficiency. (How can an
engine run efficiently when the spark event is After TDC?)
I found out long ago that running with ignition timing too far
retarded at road speed raised my engine coolant temps above normal.
(This was the result of the point gap closing up, but the timing was
nonetheless retarded about 10 deg. from normal.)
I conclude from this, and the fact that Triumph added the interrupter to
advance the timing, that retarded timing adds to engine heat at all
speeds.
So. Which one does the better job of reducing coolant
temperature...Increasing engine speed, or advancing the timing?
One way to tell would be to allow the engine coolant to go past "normal"
temp and then increase its speed to 1300 rpm thru only the throttle,
while maintaining the timing at 4 deg. ATDC at this speed. Monitor the
results.
Then repeat the process. This time just advance the timing to 10 deg.
BTDC and set/leave the engine speed at 800 rpm. Any one can try this
for himself. I know which one works better for my engine. Advancing the
timing. Speeding up the idle is a bonus.
But engines can and do idle well with the timing set at 4 deg ATDC.
Those that set their timing to this are better off if they have the
thermal switch, and it is operating as designed.
Dick
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