there was one a our field last week with the same condition, took both needels out and blew though the holes with a peice of fuel tubing and the mtr ran fine, must of had a small peice of trash in the low needle port, run a fuel filter on the engine and off of your
fuel jug, mabe this will help ,if that wont work, then take off the plate that has the needle seat in it and there is a small oval plug,drill a small hole in the center of it paying attention not to go in deep with the drill, now install a small servo screw and pull that plug out. inside you will find the ports that go to the high and low needels to the venturi, cleane that area out and make sure nothing is pluged.you can buy the small plug from most lawnmower shops that service weedeaters,had a mtr that ran on methonal and this area would get clogged often unless i flushed the carb after each flying session,hope this helps