Glad I found this forum. I hope you guys can help. I have a YG3 that I'm told is from a 2007 snowmobile. It is installed as an aircraft engine on my gyrocopter. I have the propeller pitch adjusted for 7500 max engine rpm. The engine has been working great until recently. I was climbing, WOT at ~7200 rpm. Suddenly the rpm dropped by about 400. I leveled out and checked fuel flow by changing fuel pumps, no change. It now has a noticable reduction in power at WOT with a max rpm of ~6800. I've overhauled all 3 carburetors and replaced all the rubber in them, except for the diaphrams. Replaced the fuel filters and spark plugs as well. Low and mid throttle power seems good, but the top is definitely chopped off. Verified good fuel pressure and volume. Can anyone advise me on what may have gone wrong here?