General question

[Tacklewasher]

Not sure if this should be here or in General boating, but I think my issue is motor related.<br /><br />I have a 1975 18" Starcraft aluminum boat with a 120HP OMC Stringer drive (was 140 but got repowered to a 120 at some time). Bought it last year for next to nothing and got both the motor and drive rebuilt. The whole contraption (including the trailer) weighs ~2,600 pounds loaded without people so I figure I'm 2,300 as the trailer is stinking heavy.<br /><br />Max speed for the boat is 30 mph (by GPS) and this just seems slow to me. The motor maxes out at 4,000 rpm and should be 4,600. I switched props and while the rpm's came up, I lost speed.<br /><br />My question is what should I expect for speed out of this set up. I've got a new carb on order, mostly because the one on it leaks a bit, and once that is on I'll be checking spark advance and pulling the plugs etc. I am just wondering what a baseline performance is for a boat like this.<br /><br />Thanks.