My restoration project of the 79 CX500 Custom is to the point of some short road tests. After about 10 miles of highway speed driving I thought I detected the engine starting to miss although the tach wasn't dropping off. Taking a side road at lower speed everything feels and sounds fine. Could the coils be the cause? The plugs aren't fouled, the carbs are rebuilt, the gas is fresh and the temperature is normal. I'm not sure if there are any early warnings of a dying coil(s).