Propping issue on second hand boat

[Any_Weather]

Guys, just after some advise regarding buying a second hand 2003 model 90 hp Saltwater Mercury. My brother has just test driven the said motor on a 5.0m tri hull. The maximum revs achieved was 3700rpm for a speed of 70km. It was extremelly slow take off and reasonably slow speed pickup. When taken for a water test it shook the whole outfit so hard it stalled the enging.The whole package is 2003 model with only 37 hours on the clock. What do you guys reckon.
Thanks
Lee

[Brumby]

Hi Lee,

Those revs are way too low, I have the identical motor on my old boat (Signature 492) and with an 18' prop it revs out to 5900 and about 70km/h. It is pretty quick off the mark too and happily pops my 90kg carcase out of the water on a ski.

Somethings not right with that motor - might be as simple as a bunged up carb or dirty plug, but it needs to be properly checked out, I'd want to be sure that there isn't piston damage from pre-ignition if those revs are accurate. That shaking and stalling points to not all the cylinders running cleanly - I take it the motor shook and stalled at low revs?

Good luck
Carl

[Wahoo]

Lee
that boat sounds way over propped, good top end thou
can you find out the size n pitch its running
that boat would be a dog getting out on the plane
not to good for the motor also in the long run

Daz

[Seahorse]

a 90 merc doing 70k at 3500?

[BM]

It obviously has a very tall pitched prop on it (as mentioned).

3700rpm at WOT will destroy that engine. I would be having a very careful look inside the cylinders to see what the pistons look like.

That engine is labouring badly which will cause (if it hasn't already) serious mechanical damage.

Walk away. Your buying trouble, regardless of how cheaply its offered.

Cheers,

Nicholas

[Any_Weather]

BM, mate my thoughts exactly. As soon as my brother told me about the 3700rpm I thought this has got to spell trouble. Thanks all for the replies. Looks like the deal may well have fallen through.
thanks
Lee

[revs57]

With a T Lee!!!