Is my tach broken??

[changes in latitudes]

Ok, here's the situation. I just got a 150CC (about a month ago). This is my first outboard powered boat so if this is a dumb question I apologize. I bought it used with only 4 hours on the Yamaha 50 2-stroke. I can get on to plane fine with 1-2 people and the speedo shows 31-32mph top end. So here's the question - at WOT the tach only shows about 2100 rpm. Is that possible? I have to think that the tach isn't working for 2 reasons -1. I would think that the Yam 50 should rev much higher than 2100 rpms and 2. If it really is only turning 2100 rpms how can I get 31mph out of it? Any guesses or suggestions on how I can test it? Thanks!
-Dave

[rudderhinge]

Has it been that way since day one?
If so it sounds like the tack may be set for the wrong number of engine cylinders. Take a look on the back of the tack and see what number of cylinders it is set on.
There is a small round dial on the back of the tack with a screw driver slot an a arrow pointing to numbers . Make sure that it is pointing to the same number of cylinders that your engine has. If it is set on the right number of cylinders then I would take it back to the dealer. Hope this helps. Let us know. Bob

[cagrove]

Here's a couple of files from Faria...the maker of most of our tachometers. One file gives general installation information on installation, use and set up. The second gives you the correct number of poles on the alternator of your engine so you can set the switch on the back of the tach to the correct setting.

I hope this helps.

[changes in latitudes]

Thanks guys! I'll take a look at the back of the tach and let you know what I come up with.
-Dave

[jmuduke]

Same thing happened to me on my 2007 170 CC. The boats are coming from the factory with the tach rigged for a 4-stroke and not a 2-stroke. The setting on the back needs to be set from position 5 to position 2. The change takes about 10 minutes. Use a small screwdriver and push the pin in and turn it to the new number gently. It should be fine going forward. Good Luck!!!

[changes in latitudes]

Thanks for the help guys! It was the setting on the tach, but it wasn't as easy to fix as I expected. It seems I have one of those new fangled Yamaha digital tachs so it didn't have the dial to choose the # of cylinders. Instead it had a series of 3 up/down switches that needed to be set. Fortunately I found the schematic online - I'd thought I'd post it incase anyone else has the same problem. Thanks Again!
-Dave

[cagrove]

Thanks for sharing what you found...I'm sure others will find it helpful as well.

[paulgw]

My tach, a Faria analog - 4 stroke Yamaha 50, sometimes reads at 2 times actual speed. Idle at 1600-2000 and throttle cracked 3500-4000. Then the next time I look it is a normal RPM. Have 30 hrs on this motor and only noticed this the last 10 hours or so. Most of the time it's right.
Any ideas?
Thanks

[Putershark]

That sounds like either a loose ground wire, or a Tach in the early stages of going south