If it's warmup related consider this. The Bosch CDI unit can go bad where it "locks up" and stops producing sparks under temperature stress. Once you turn the ignition to OFF it resets the box and it will work again for some period of time before the cycle repeats. The effect is strongly temperature-dependent.
To test whether lock-up is your problem do this: Once the car shuts down DO NOT turn off the igntion. Open the engine lid and listen to the whine of the CDI box and memorize its tone. Then turn the ignition to OFF and back to ON without starting the engine. If the whine now sounds different (lower pitch and louder) you have identified a lock-up condition.
If the whine sounds about the same after the power-cycling it confirms that lock-up is not your source of the problem.
Friday, May 25th, 2012 AT 6:46 PM