lack of power

[Fippe]

Hello,

I have a mercruiser 5.7 2bbl mercarb thunderbolt 5 wo knocksensor in a maxum 2400scr from 97.
I have rebulit the engine after a blown headgasket,
when i bought the boat it only rew 400-4200rpm and I thought that after the rebuilt it would work fine, but I was wrong it still only rews 4000-4200 on wot
to make shure that the ignition works fine i hade a mechanic too adjust the ignition and after that still no difference,
now I also have changed the fuelfilter, rotor, distributor cap and cables,
when I did that I noticed some rust on the sensor in the distributor, cleaned it up a bit an still no difference.
the only thing I haven´t done now is rebuilding the mercarb and looked att the antisyphon valve.
the engine runs fine good trottle response and always starts fine,
when i changed the fuelfilter i noticed that it dosn´t smell as much as it used to do, when I look at it in a glas it looks fine, i use 95 octane gasoline (sweden)
is it posible that the antisyphon valve or the carburator makes the engine not have the power it use to have,

the propeller is a quicksilver 4blade 16p