Merc 90 over rev

[tracker2]

Checked out 19 pages on a search with no luck.

Here's the problem.. 1999 Suntracker, 21' Party Barge. 1999 90 H.P. 2 stroke Merc. Running a 13-3/4 X 17 Vortec prop. WOT is 6100 RPM. Engine is supposed to be in the 5000 to 5500 range. My question is .. Will a 19 pitch bring the R's down in range or will I need to go to a 21? This is light load with 3 adults and small child... Don't have a speedo or GPS so no speed is known. Any suggestions?

[cwag911]

Are you sure your tach is correct? A 17p on a 90 HP motor sounds like too much prop and shouldn't give you that rpm unless the prop is slipping or cavatating.

[Bamaman]

Carl might be right about the tachometer. You might want to have it checked for accuracy.

The current Mercury 90 hp 2 stroke is running a 2.33:1 gear ratio which would mean it may use a propeller with high pitch.

FYI: A Mercury 115 hp 2 stroke has a 2.07:1 gear ratio and they'd run a lower pitch prop since the prop's turning over faster. I

But if your tachometer is correct, you probably need more pitch to bring the rpm's down to 5500 ish.

[slingshot]

Just remember, for every inch of pitch you adjust, you will effect your RPM by about 200.

[tracker2]

OK, Houston, we have a problem. After borrowing a gps, I find wot speed is 14.3 mph. tach is reading 6100. Upon idling down and kicking out of gear, tach is reading 2000. First problem first, I got to get a new tach. Then back to the prop.....Thanks all...

[jrolin1]

Most outboard tachs have a switch on the back for you to set the number of cylinders the motor has. You may want to check that before replacing it. Even if it is set right I would change it and then change it back to see if that helps.

[tracker2]

Never gave the switch a thought. Good idea. Also have a strong suspicion that the hub is spun on the prop. Even tho it is new.
Has anyone had an trouble with the hub on the Vortec props.

[mike]

yep, check the switch on the back of the tach. Mine was set wrong when I got my toon.