89 40HP Tiller power lose, Im am stumpt.

[jeepv8pwr]

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

[99yam40]

timing is easy to check with a timing light, why not check it just to make sure it is in spec?

The light will also show if spark is dropping on a cylinder if you move the light to the different plug wires.

Fuel pump leaking into the crank case due to pin hole will cause a rich mix that can cause a cylinder not to fire properly, check it to see

[rodbolt17]

fuel pump or the fitting at the quick connect has a swelled oring restricting fuel.

the pulse diaphragm fuel pumps don't live forever.
any green gunk in the fuel bowls and guess what, you also have green gunk in the fuel pump waiting to re-foul the carbs.

[grouper sandwich]

Check your CDI. I just went this with 1993 70 and it ended up being the CDI. My symptoms were almost exactly the same as yours. I chased the mythical fuel ghosts for over a year. I can almost guarantee your CDI is your problem.