I picked up a '96 Baja Islander 272 open bow that had a broken 454Mag in it and replaced it with a 502/502hp marine crate motor with an 850 double pumper running a 23p Mirage Plus 3 blade prop. So far with a half tank of fuel and 4 people on board the best I've gotten out of it is an 48mph on the iPhone GPS and topped out at 4800rpm regardless of trim. All of the OEM propaganda that I've read shows these boats doing 60+ with the stock 454.

Am I missing something here, or is this inline with what to expect with this boat?

Thanks.

Something is definitely off. I run faster than that in my 292 Islander with 496HO/B1X spinning a 22p Bravo or 21p Mirage Plus (verified with scanner & GPS).

With a stock 454 should be 58-60 MPH. What drive ratio do you have? Did you build the engine or buy used with those specs? Leak down and compression test? Jetting? Secondaries operational? Something is definitely not right at 48MPH.

That's what I thought. I think I need to check the secondaries. When I bought the boat it had a pumped up 496 truck motor with a flat cam and broken lifter, but I did give it a run with the new carburetor and it would "choke" when the secondaries opened up. I just thought it was due to the limping motor.

This is the motor in it that I bought off of another member here on the board. It otherwise runs great.

http://www.offshoreonly.com/forums/s...pan-fresh.html

I did check the throttle throw and the mechanical secondaries are opening. I'm curious if the Holley red fuel pump is inadequate? 67gph at 5psi or 97gph at free flow.

Have you verified ignition timing?

I had a local performance boat shop swap the motors, so I'll ask him if the ignition was working as it should. It does sort of act like it's not advancing. He has an excellent reputation but was rushed as he was trying to get on with his own holiday.

Timing was verified to be working, and the secondaries are squirting as it they should. I'll play with the jetting, but it looks like it's just time to play with the prop.

It also just occurred to me that I'm still running gas from last October with no fresh addition. Could that be a reason for decreased performance, or are these motors pretty hearty?

If its almost year old gas with no stabilizer, i would drain it and add new.