I switch my feul from 10% to 15% on the advice of my lhs. Last night i ran the last of my 10% and all went well. when i filled the tank with the 15% all I could do (if I could get the plane of the ground) was practice dead stick landings. I tried to adjust theneedle valve, on the bench it would run fine. it ran at idle or full throtle even pointed strait up. If I put it on the ground it may stall after I taxi to the runway or if I reduce the trottle while flying. It is getting colder here about 45 degrees but the first tank (10%) ran well and I was told that the 15% would run better in colder weather. havent seen anyone at the field for a few weeks now so I could use some advise. Thank you