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Backfire
- Thread starter Chris Costello
- Start date
My '76 does that too. I've just taken it on as part of the charm of riding an old bike.....
Undoubtedly, it's some sort of an air leak somewhere.....
Sounds like unburned fuel is igniting during the wasted spark near the end of the exhaust stroke. I bet it wouldn't do that with dual ignition.
The stress on the ignition is higher during the compresson stroke, much less during the exhaust stroke. The plug may be misfiring on the compression stroke, and firing fine on the lower-pressure exhaust stroke. This line of thinking means new plugs.
If the coil has an internal problem, a simple test would be to swap the plug leads. If the popping swaps sides, suspect the coil.
Or, it could be that the carbs are out of sync...
The stress on the ignition is higher during the compresson stroke, much less during the exhaust stroke. The plug may be misfiring on the compression stroke, and firing fine on the lower-pressure exhaust stroke. This line of thinking means new plugs.
If the coil has an internal problem, a simple test would be to swap the plug leads. If the popping swaps sides, suspect the coil.
Or, it could be that the carbs are out of sync...
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