2004 Mercury 75 ELPTO - low on power -

[Bannister 6905]

My 2004 Mercury 75 ELPTO starts and idles fine, but when last on the lake, it would not plane the boat out normally - with some playing with the trim and choke, I finally was able to get the boat on plane, but it would not rev past 4000 rpm. No missing, no unusual sounds. I even tried to trim the boat out until it cavitated, and even then, it would only rev to 5000. Fuel and lines are new, new fuel pump, plugs and filter. Compression was even across all 3 at 100psi. All 3 cylinders are firing, as confirmed by connecting a timing light to each. When running at 4000, it was smooth, with no surging or other issues - just VERY doggy. Prop is correctly sized for the boat, as well - 21 pitch on a 16' Nitro 640LX bass boat.
The prior owner may well have screwed with the timing, which I am going to check next...
Any other ideas as to cause would be appreciated!
Bannister

 

[ondarvr]

Is this a new issue, did it run correctly before, or did you buy it this way and just found out about it?

 

[Bannister 6905]

Timing was OK - decided to remove carbs and check for debris...top 2 cabs were fine, but found the fuel inlet elbow CLOGGED with what looked like sand and dirt on the bottom carb. Very difficult to remove, but after several shots of carb cleaner and compressed air, the clog blew out all over my shirt! The motor now runs perfectly. The boat had sat unused for an expended period of time, without the carbs being emptied. I added a separate fuel filter just in front of the bulb to prevent this in the future.