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CB400 Tach / Pulse per revolution

5.2K views 8 replies 4 participants last post by  J-T  
Your bike fires each plug once per revolution. Even though each cylinder only fires every other revolution the ignition system fires both plugs every time, hence the term "wasted spark ignition".

I can't imagine why an ignition system would fire a plug twice per revolution, are you sure it doesn't say 2 revolutions per pulse? The one pulse per revolution setting would typically apply to a 2 cycle engine (common on vintage dirt bikes), the 2 revolutions per pulse setting would apply to 4 cycle engines.
 
No, the "wasted spark" ignition fires both spark plugs at the top of each stroke, there is no spark at the bottom of the stroke. In our SOHC engines the pistons move up and down together rather than opposite each other. When one piston is rising on it's compression stroke the other piston is rising on it's exhaust stroke. As the pistons approach TDC both plugs fire. The plug that fires on it's exhaust stroke is the "wasted spark".

Let us know how the 2P/1R setting works out for you.