Merc 140hp no power and won't go over 3000rpm??

To start off, I have an '81 glastron Carlson with a 140hp 181ci 4cyl. Would not start at beginning of season, so we replaced condenser, distributor cap, and points. It fired right up. Burned out the old gas, as it was running poorly, and did so with a bottle of seafoam in the old gas along with a few gallons of fresh premium. Now after filling with fresh premium and another seafoam, it ran better, but still did not have much power. I changed spark plugs, fuel filter, an had carb rebuilt. Gap was set correctly with feeler gauge on distributor, and plugs gapped correctly as well. I've also checked the strainer on the carb and the anti siphon valve on the fuel line, and both seem to be ok. Taking tomorrow morning to make sure timing and dwell are correct. The boat will not go much over 3000rpm, and the tach kind of bounces around at wot. Usually this boat will run 50+mph, but has a horrible time hitting 40 right now. It will rev past 3000 in neutral, but has no power under load Not sure what it can be. It still starts great, just seems to almost lose power once on plane, and I'm out of ideas. Can anyone help? I'm so frustrated.

Re: Merc 140hp no power and won't go over 3000rpm??

have a look at item 13 from this list.
ya might give the trouble shooting guide a look from here.

either/or may give ya some ideas....

Re: Merc 140hp no power and won't go over 3000rpm??

It starts right up with muffs, but seems to have an intermittent miss while running too