Quote:
Originally Posted by Bob Ashlock
Answering your earlier question about the 'runs fine for 30 min' ... I was trying to start off with the basic stuff first, checking power integrity and points as you initially commented that the tach was jumping around. Does the tach actually behave 'fine' for the first 30 min and THEN when the problem begins does the tach jump come into play at the same time? Is that a kind of 'violent' jumping or just a 'dipping' as the engine starts missing? One of the most common CDI failures is the discharge capacitor shorting or opening after the unit heats up. Of course this kills the spark, and the tach is going to start changing as the rpms come down. I think a checkout of the CDI is in order and there are others on this forum that have bench test setups to do this, as I also do. Running hot on a bench test usually exposes this capacitor problem right away. And then of course you still have what appears to be an alternator issue to contend with. The suggestion by others to monitor the 12V is important because if your alternator is going berserk and putting out higher voltage or the dc voltage is carrying a large ac component (bad diode?) then the CDI unit will be dissipating more power, getting hotter than usual, etc., all aggravations of the problem.
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Hi Bob,
Thanks for the explanation that really helps. I will check everything. Did some testing yesterday.
To answer your question, the tach runs fine for about 30 min. After around 1520 min, the engine starts cutting out for about a second at a time, and eventually it just shuts off completely after roughly 30 min from startup. Yesterday when I tested, the tach stayed mostly steady with just a couple of small jumps.
I also checked battery voltage:
Idle: 12.4V
2000 RPM: still 12.4V
Engine off: 12.6V
All measured at the battery posts. So this means that the alternator doesnt do the job. Could this relatively low voltage also be whats causing the engine to die after 30 minutes?