2 stroke engines need back pressure
Absolutely not. Two-stroke engines usually improve power with a "tuned" (resonating) exhaust--they're said to come "on the pipe" the way 4-stroke engines are said to come "on the cam".
If the pipe is tuned properly, the exhaust resonance produces a low-pressure spike at the exhaust port just before the port closes, to draw-in additional fuel/air mixture.
It's the LACK of pressure (vacuum) AT THE RIGHT TIME, caused by the resonance that improves two-stroke power. Which is also why 2-strokes tuned like this tend to be "peaky".
I took lip stick and put a line from where the primary’s went into the collector all the way to the end. Where the lip stick stopped burning that’s where I cut them. I don’t remember it making a difference.
I've heard multiple variations of that story--you say lipstick, other guys use tire crayon, some folks actually use a fancy temperature-indicating marker.
Point is,
temperature is not what makes a tuned exhaust.
Resonance is, so the mathematics of the speed of sound is involved, which varies with temperature, humidity, and other factors including whether you're tuning for the first peak, second peak, third peak, etc.
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I just love a flatty with a visible fin. You've just made me moist. I don't expect my '73 Sanger bubbledeck ski-boat does that often...if at all. And certainly not for the last few years--hasn't been on the water in near a decade.