a broken impulse coupling will do that. Best to check it if your mag is the impulse variety. Wasted spark is on the exhaust stroke, with no compression, so that is not your issue. A/F mixture cannot be lit by a spark plug unless the mixture is significantly compressed.
If the backfire was due to slow rotation speed, how would it be possible to hand start an aircraft engine?
larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 08-05-2020 at 11:13 AM.
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