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 .