ORIGINAL: speedster 1919
I have a 50 and an 80. The 90 is suppose to be a bored out 80 . The 80 was very tight and did not like high nitro. Super Tigre OEM plugs are poor and and don't last that long. The SK is alittle hard to tune but they run good. They are not super power houses. That 15x6 is got to be too large a prop and 7500 too low for a 2 cycle. A 12x8 MAS will be the perfect speed prop .
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Lately I have read of more ridiculous advice given by tech support people than I ever thought was possible. Who would recommend running a 15x6 on a .90 two-stroke during break-in, or any other time?
Ringed engines should be ran in a rich four-stroke during the first several tanks of fuel. ABC engines are ran in a rich two-stroke during break-in.
A 12x8 or a 13x6 would be about the perfect prop for breaking-in this engine. A 14x4 is okay too, once it has some time on it. You don't want to lug a glow two-stroke engine down much below 10,000 rpm at W.O.T. Gasoline engines are a different matter, their timing is adjusted for lower rpm. Adjusting a glow engine's timing is not such an easy matter and can lead to preignition/damage.