Tachometers not in sync

TADTOOMUCH · Post by **TADTOOMUCH** » Sun Jun 05, 2011 7:17 pm

My tachs both do not read the same on both engines when I have them running at same RPM. The port reads correct on the upper helm and the starboard reads high. Then when I go below those don't agree with the upper helm. Any suggestions on how to adjust them. I have the original AC Datcon tachs on my 1978 F-32.

I tried to adjust them to be correct at 1000 rpms at the dock but they are almost 800 rpms off from each other at cruising speed.

prowlersfish · Post by **prowlersfish** » Sun Jun 05, 2011 7:35 pm

Some tachs have a adjustment screw on the back , also check the grounds to both . your tach(s) could be just getting tired .It a wonder they last as long as they do on the uper helm

Big D · Post by **Big D** » Sun Jun 05, 2011 9:00 pm

There should be a cylinder selector switch at the back of the tach, switch it back and forth several times, return to original position (8 cyl ?) and try again.

TC · Post by TC » Sun Jun 05, 2011 9:45 pm

My tachs did not agree at 2600 - 2800 rpm they were about 200 rpm apart, the starboard engine showing the faster speed.
This spring I was changing the dash indicator lights and had the cluster tipped out to this. Now's my chance. I started both engines and brought the starboard engine to cruise speed ( 2800 rpm ) then brought the port engine up in speed until the synchronizer showed "O" and the engines did sound "right". At that point I adjusted the port engine tach to agree with the starboard tach. If you look at the rear of the tach you will see a small adjusting screw.
Now I can hear the comments, "How do you know the starboard tach was correct?" I don't. I just feel more comfortable reading a tach that may be indicating 200 faster than the possibility of an engine running 200 faster than indicated.

prowlersfish · Post by **prowlersfish** » Sun Jun 05, 2011 10:16 pm

if the tach reads low you could turn more rpm then you think . If it reads high you could be over loading the engines and not know it ( failing to reach full rpm) On a diesel I will take I rather be turning more rpm then over loading it for sure . On a gasser its a toss up . Best to get it right check them with a photo/laser tach .

mhandley · Post by **mhandley** » Mon Jun 06, 2011 9:16 pm

Is it typical that you all use your analog tacho's?

My 10 meter has those, but, as most of you have stated, they're not the best.

My hole in the water came with a digital synchronizer which gets them dead nuts.

Anyway, I'll bet that digital unit is pretty cheap.

prowlersfish · Post by **prowlersfish** » Mon Jun 06, 2011 10:00 pm

You could not give me a digital tach,