www.iFourWinns.com

In order to get the syncro gauge to zero (vertical) I have 3725 (left tacho) and 3600 rpm (right tacho)
However I have the best aural balance (no harmomic) with 3675/3600 set. This has syncro a few notches off centre.
Something doesn't quite seem right.....
I believe the tacho's take their feed from alternator RPM?
Sync gauge is probably just reading phase difference between L & R?

I fly light twin aircraft and used to tuning with a sync gauge, so something just doesn't seem right here.
Opinions and ideas most welcome.

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GI Auz
2004 288 Vista
Twin 4.3 Merc


Previously:
Beneteau 411 Non-Stink

I believe the sync signal is taken from the ignition system of each gas engine. It's either that or an engine rpm sensor commonly used in the modern computer controlled engines. There is the possibility of alternator belt slip, and the alternator does not have a pickup or terminal for the alternating current before going thru the rectifier and being converted to direct current. If possible, check the electrical connections and also verify tachometer and sync gauge accuracy. You might check with the sync gauge manufacturer or a manual to see if the gauge can be adjusted. The tachometers, like many other gauges, can be off by more than many people would believe. In my days of working on aircraft I've seen tachs off by 100-200 rpm. We'd like to think they are a precision gauge, but they are not always.

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Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon

I found this in the Faria sync gauge manual:

10. Calibration: This gauge has been calibrated at the factory,
and should never need adjustment. An exception to this is a diesel
engine application where the alternator is the tach signal source.
Due to variations in belt tension, and/or belt dimensions, engine
alternators may actually spin at different speeds with the engines
running at the same RPM’s.
If you are experiencing problems with this type of application, the
synchro can be adjusted to work with these differences by slightly
rotating the adjustment potentiometer with a 5/64” Allen wrench.
This adjustment can also be used to fine tune a synchro in any
application.

web site with link to manual: http://faria-instruments.com/manuals.php

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Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon

Great work - thank you!! I will calibrate that sync gauge. And I agree, the tacho's may be out by a bit as well.

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GI Auz
2004 288 Vista
Twin 4.3 Merc


Previously:
Beneteau 411 Non-Stink

My engines are in sync at low rpms and then go their own way at higher rpms so how can you adjust that? I find most gauges on boats not to be very accurate and really only pay attention to the oil temp and gas gauges. I use my ear gauge for syncing the engines and eye gauge for trimming the outdrives.

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Current Boat: 2000 Four Winns 298 Vista
Previous Boat: 2000 Carver 406MY

According to my ears, my sync gauge is accurate, but my tach's read ~150 RPM different. I figure the tach calibration is off in my case.

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1969 Chris Craft Commander 47
1999 Four Winns 328 Vista - SOLD

You can buy a cheap laser tachometer. I think I paid like $15 or $20 or so. You stick a piece if reflective tape on the crank and point the laser at it. Pretty much can be used on anything because has nothing to do with the engine electronics. I use it more for small engines without tachs.
Do a search on amazon for "laser tach" you'll see tons...

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--2002 3880 Regal Flybridge | Twin Merc 8.1HO **Seven**
--2003 AB 13 VST Console Inflatable | Tohatsu 40hp TLDI **Phish'n ski**
--310 Mercury Inflatable | 1982 9.9 Johnson

when I first got my boat the tachs would seam to work fine then one or the other would just start going crazy I removed the dash panel and found all the wires on the back of the tachs where loose I would check , clean, and tighten all the conections before doing anything

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2005 vista 288