I have a 4-yr-old 46AX that has a lot of use on an Ultra-stik. It has just developed a power problem that shows up with a very narrow tuning range. My range on the high rpm adjustment needle is only about 1/4 turn total between rich or lean where the engine will even remain running much less running on the rich or lean side. I'm able to get about 11,800 rpm out of it. I've been running an 11x6 prop since I had the engine with no changes. In the air, the plane has noticeable less speed. When cold, turning the prop doesn't seem to have the same resistance as it used to. Any advice would be helpful.