can you advance it to full throttle? If not, try it with the glow driver on. Tune the high end first. You'll need to do this using a tach, then richen it up until your RPM drops by about 200 rpm. Then slowly lower your throttle to idle. If it surges after you hit idle, the low speed mixture is too lean; if the RPMs slowly drop after hitting idle, the mixture screw is too rich.

Make sure you're not over proping it and running good fuel as well, or else you'll never be able to tune it.