Balance
Your CG should be right on the front spar. With that balance point your elevons should be very close to level, meaning perfectly streamlined with the wing. The Dust normally does not fly with any up elevon.
It sounds like your Dust is nose heavy which requires a certain amount of up trim or up elevon for level flight at 1/4 throttle. As soon as you hit full throttle and increase speed the up elevon causes the pitch up.