Sounds like your landing gear is too short. It probably bent from some previous landings. You need to tweak it back so the legs are a bit taller and the wheels a bit closer together.

As Steve mentioned in his 6 point list you need to open the needle up so it starts rich and then lean it out to make the sound of the exhaust as high a pitch as you can then back it off a hair. And try running it for a couple of tanks on the ground to make sure it runs out the whole tank at the full RPM's. If it's hard to peak out or seems like the needle valve needs to be adjusted to keep it running with lots of large changes in the RPMs while running then it may need some cleaning out, the needle valve tip may be bent or the reed may be deformed or worn out.