High RPM's

(mikef9844) · (mikef9844) **Join Date: Sep 2008** 02-12-2009, 7:24 PM

I just did the Wide Open Throttle test today with my boat. It has a Mercury 185hp engine and a 14x19 3 blade prop. I had no weight in the boat, 3/4 full tank, and 2 people. At WOT the RPM's got to 6,400! The rated range for WOT on my engine is 4400-4800. At wakeboarding speeds (20-22 mph) it runs around 3200-3800. I was planning on getting a new prop based on this test but I can't believe how high the rmp's got! Can anyone give me any insight to this and what I can do. Is it possible the RPM gauge is off? Also, idle RPM's run about 1200 and the rated idle RMP is 600.

(raftisland) · (raftisland) **Join Date: Aug 2006** 02-12-2009, 7:32 PM

one of my friend has an I/O Glastron and i used to tow him at 3400 rpm's.

(brucemac) · (brucemac) **Join Date: Dec 2005** 02-12-2009, 7:40 PM

/edit

most i/o's have some sort of safety mechanism, i.e., rev limiter or even simply a warning buzzer (maybe that's unplugged?). 6400rpm sound way too high, but then again, so does idle. defer to either a prop shop, dealer, or the mfg or find out how to test your tach.

(Message edited by brucemac on February 12, 2009)

(bftskir) · (bftskir) **Join Date: Jan 2004** 02-12-2009, 9:16 PM

sumpins not right

(mikeski) · (mikeski) **Join Date: Aug 2003** 02-12-2009, 11:07 PM

6 cyl motor, tach in 4 cyl mode? RPM reads 150% of true reading?

(rallyart) · (rallyart) **Join Date: Nov 2006** 02-12-2009, 11:17 PM

Your running the Merc 4 cylinder 485 right?
Did you change the Tach? It might be a tach issue but that engine is capable of running that fast although it would normally take a 17 pitch.
Has your prop been repaired several times so that it might be a smaller diameter than in used to be?
Also how big is your '84 boat?

(Message edited by rallyart on February 12, 2009)