I too have a SK 90 and it runs so nice but did have one problem it would slowly lean out when in the air. No mater what we did it still would lean out and heat up but never dead-stick so I called the Tech. support and asked them and this is what they said. The first thing he asked was what prop I had on it and I told him it was a 14x8 mas and was told that it was to small to go to a 15x6 or 15x8 . what was happing was that in the air it would unload and get over 11000 rpm and it is not ported for RPM over 11500 so it would lean out once I put on the bigger prop no more lean condition and runs like a champ.