chris craft scorpion
 

I've got an 1986 chris craft scorpion 210 runs very Good and looks brand new but will not run over 35mph is this normal?

I'd say that sounds low, What engine/drive?

I would think 45-50 MPH with a SBC.

Does it have bottom paint? That can scrub a substantial amount of speed, as can the "shag carpet" from sitting in the water.

Otherwise, I would think sick motor or wet transom and stringers.

The outside of boat is factory no "shag carpet" garage kept. The motor is a mercruiser mcm 260 ( Chevy 350) some specs off valve cover says maximum rpm at WOT is 3500 260 horsepower. The motor doesn't seem to be running rough at all and starts right up I just wasn't sure of top speed as this is my first boat.

The drive is also mercruiser and I'd imagine it's the factory engine and drive from 1986. Guy I bought it from had all records of maintenance being done by a marine shop and he also said it's never ran over 35 for him. Hell the Speedo could be broke idk.

I was wrong 4200-4600 rpm at WOT

Have you had it running 4600 RPM ?

Definitely need to get some solid measurements here to have any chance of sorting this out. As you noted, it's not clear if the speedo works or doesn't etc.

1. Download a speedometer app for your mobile phone. If you don't have an Apple or Android phone, I'd borrow one.
2. Safely make two WOT runs, in opposite directions on the same stretch of water. Get speed off the phone, and RPM off the tach while settled at WOT. (The reason for two in opposite directions is that there could be significant current or tide. It's PROBABLY not critical, but you might as well do it right. I've boated some places where there was current of 4-5 knots.)
3. Find out the pitch of your prop. Should be able to look over your prop for stamped markings that indicate the prop's pitch.
4. Find out the gear ratio of your drive. This one can be harder, but you should be able to find model/serial markings on the drive. Worst case, you can check it mechanically, but before worrying about that, I'd see if you can read the markings. (I have owned drives where there was enough paint slopped on that a little sanding was required to read the numbers.)

Lots of things could be wrong. If we have good measurements on the above we should have a much better idea whether the motor is sick or the boat is heavy, whether your tach or speedo is likely to be way off, etc. At minimum, without good measures of speed and RPM, we're totally stabbing in the dark.

Mike

Use the speed app on your phone. Factory speedos are notoriously wrong.

You should be turning 4500-4600 rpm. Check your prop also, is it bent, etc...

Also are you probably trimming the boat?

Not sure if I'm trimming boat correctly. But I took it out on Sunday used as pedometer on my phone and Speedo is correct it won't go over 35 and it won't go over 3000 RPM I have a 21 pitch prop on the boat and the motor seems to be running just fine not sure if it's throttled back don't really know

that pitch sounds about right.

More than likely you got a tune up issue. Get new plugs, wires, cap and rotors, job should be able to be done in an hour or so. Take off the flame arrestor clean it with break cleaner. Lastly check the PCV valve, take it off if it rattles your fine, otherwise replace.

Plugs wires, cap and rotor under 100 bucks.

Lastly get some fresh non ethanol gas and run some star tron or sea foam. More than like this will fix the issue

Please describe how you are trimming.

Padraig

Sounds like the motor is not putting out much power, whether because of ignition issues, fuel issues, throttle issues, whatever. Based on your description of the boat it doesn't sound like a drag issue.

Sounds like it may only be running on the primaries( have carb checked) Good Luck!!!