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Glyn Chambers

There are many contributory factors that cause spitting back,it seems to occur in low compresson early engines.However there is one primary cause as Bob Brougham found out.When one cylinder is exhausting flaming gases, some of the flame goes straight into the other cylinder which of course still has its exhaust port open as its piston is coming up on compresson with of course a full charge of unburnt gas in the cylinder.The exhaust ports need to be kept apart from each other.I have read an article written by Rickardo ( yes him of 4 valve fame) before the 1st world war in which he stated that the exhausts from multi cylinder 2 strokes must be kept as far as possible from each other..
Bobs solution was to make a exhaust stub with a divider in it profiled back into the cylinder block so that the gases went their own way into the exhaust pipe and not tracked across into the other cylinder.I had this done to two of my engines and it utterly transformed them.
NOTE Pickardo made the worlds most powerfull aircraft piston engine a 2 stroke !.To late to be be put in production as the Jet age took over.