5.7 350 lack of power

[thagan03]

I have a 21ft Mariah shabah with a 5.7 mercruiser 19p stainless prop, I bought the boat earlier this year, with 1 or 2 people in the boat, it planes out fine and would run about 38-40 at 3300 rpm, which I thought was low to begin with, once you put 5 or 6 people and a couple coolers, it takes forever to get on plane and usually have to move people up front, I ordered a 15p prop and a little better but still not satisfied, I now run 3800 rpm and only about 33 mph, not sure what could be wrong with it any help is appreciated, also has a fresh tune up

 

[kenny nunez]

One of the first things taught in service school. "Make sure the throttle opens the carberator all the way". If you have a Quadrajet be sure the air valve is opening @ full throttle. Does the boat have water trapped in the hull? Is the carberator the correct marine type? Flame arrestor not restricted. Is the timing set to spec?
I am sure I left some things out and more people will chime in.

 

[Rick Stephens]

Pretty good list from Kenny. I would add that with normal load your engine should easily get up on plane and at WOT hit 4400 to 4600 RPMs. If you are stuck in the mid 3k range then check drive gear ratio along with engine stuff noted by Kenny. If the gear ratio is too low for your motor it will.be lugging.