I'm no expert on this, but I do know that there is a period during which both the intake AND the exaust valves are partially open at the same time. It is called valve overlap and it is designed into the cam. The idea is to let the shockwave from the exhaust leaving to create additional vacuum for the intake mixture.
If there is a mechanic out there, can you please weigh in on this?
1998 Honda Shadow ACE 750
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