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CRF450 Ignition Question

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I am in the process of replacing both intake valves on my 04 450. In the process, I got to thinking. The bottom end of the motor doesn't know the difference between TDC on the compression stroke and TDC on the end of the exhaust stroke. Does this mean that the spark plug fires on each revolution?

Without a crank or cam position sensor, the ignition control module doesn't have enough information to discern between compression and exhaust strokes, so I assume that the spark plug fires on each revolution. Is this correct?

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Yes, you're right. Usually most four stroke motors with completely electronic ignitions (no distributor) fire a spark every revolution; one on the compression stroke and one on the exhaust stroke.

Chris.

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They have to to know what rpm the engine is turning so it knows what the spark lead needs to be on the following revolution. It senses tdc on every revolution then calculates how much lead to give it. Ignitions without microcontrollers trigger when it needs to fire and even older four strokes have the trigger on the camshaft, which turns at half crank speed, so they only fire every other revolution. Some Honda's with older designs are still like that, I believe.

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