there's an outside chance you have a defective (but not completely broken) coil. It is common in motorcycles especially to have this problem. What happens is that the coil works just fine when 'cold'. After the engine bay warms up and the coil pack warms up, it starts getting flaky and eventually non-operational coil until it cools off. Seeing as your car *has* cooled off, and you're getting a weak spark, this may be something to check.