89 Pro40 tiller, engine originally ran great. Recently it began to lose power once on plane at WOT. I have cleaned carbs thoroughly, there was a bit of green gunk in there from old gas. Figured that would solve the problem but no such luck. The engine idles great, starts great, even sounds great. Sometimes it will run for 10 minutes at WOT without any issues, other times it will get on plane and gradually start losing power, almost like the throttle is being turned down. There is no miss firing or abnormal noises I can hear. Compression on all three cylinders is approx. 115 psi. I tried a new clean external tank with new line and primer, also a new fuel filter. No luck. still doing it. plugs look good, kind of dark tan colored. Oil injection is still in use. I am stumpt, this is one of the better running outboards I have every used but the stupid thing just keeps on randomly losing power once on top end. there is no back firing, no fuel leaking, no gaskets or related visibly leaking. I am typically quite mechanically inclined but cant figure this one out. Maybe timing but why would it randomly adjust timing like that. Coils I assume are good because there is good spark and even once it begins to lose power and I put it back to idle it will idle all day like that without missing a beat. Please Please Please help, I cant afford a 5k dollar motor. HELP