I have a ys 63 engine it is new but has about 1 gal of fuel through it. the engine transitions well from low to high and has a good top end. The problem is that when the throttle is advanced a little below 1/4 and left there the engine load up with fuel. upon pushing the throttle to full it takes about 3 to 4 seconds to clear and run fast. at all other settings though letting the engine run for awhile does not cause this problem. Even letting it run at idle for 30 seconds I can still get a fast good transition. Any clues to what is wrong or needs to be adjusted?