Re: not enough backpressure?
First, Tom and George, the 2 strokes do not use exhaust back pressure they use sound waves to control the cylinder scavenge. This is why the muffler is shaped like 2 cones welded together at the big end. I found out how to tune 2 strokes running them back in the day. We used to make our own stingers to get the best performance from the 2 stroke racers.
Second, the reason a pietenpol runs good is the carb is tuned to the engine without exhaust and the engine is mostly run at a steady speed not up and down like a car. If you run the throttle up on any motor without a muffler or with straight pipes slowly it will respond without problem. It is when you stab the throttle that it hesitates and splutters.
I don't think the problem with this motor is back pressure because even a straight pipe with a bend would present enough to make it run OK.
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