penbroke
05-12-2003, 09:26 PM
If your old tach reads wrong (usualy too high) and looks like this:
http://www.donzi.net/photos/penbroke_tach_1.jpg
The label may be different but the inside most likely looks like this:
http://www.donzi.net/photos/penbroke_tach_2.jpg
The dark blueish round object with the screwdriver slot in the upper right is a potentiometer (pot) which allows calibration of the tach.
It can be accessed with a small screwdriver thru the hole indicated by the arrow. Just peel of the sticker covering the hole.
http://www.donzi.net/photos/penbroke_tach_3.jpg
Hook up a (known) accurate tune-up tach and adjust the pot 'till the boat tach reads the same as the tune-up tach. Get the boat wet and compare the two at several engine speeds. They probably won't be in complete agreement but I was able to get mine to read within about 100 rpm across the whole range. The top end of the range is probably more important than the bottom. Before the final setting, rotate the pot several times back and forth to rub the contacts clean.
Be sure to replace the sticker over the access hole to keep the bugs out.
Keep a close eye on the tach and make it earn your trust before you "rev it on the red line". Actually if you are pushing your luck rpm wise you should be using a better quality tach anyway.
TRY THIS AT YOUR OWN RISK!
No guarantee but it worked for me!
Frank
Trying to keep the old stuff working.
http://www.donzi.net/photos/penbroke_tach_1.jpg
The label may be different but the inside most likely looks like this:
http://www.donzi.net/photos/penbroke_tach_2.jpg
The dark blueish round object with the screwdriver slot in the upper right is a potentiometer (pot) which allows calibration of the tach.
It can be accessed with a small screwdriver thru the hole indicated by the arrow. Just peel of the sticker covering the hole.
http://www.donzi.net/photos/penbroke_tach_3.jpg
Hook up a (known) accurate tune-up tach and adjust the pot 'till the boat tach reads the same as the tune-up tach. Get the boat wet and compare the two at several engine speeds. They probably won't be in complete agreement but I was able to get mine to read within about 100 rpm across the whole range. The top end of the range is probably more important than the bottom. Before the final setting, rotate the pot several times back and forth to rub the contacts clean.
Be sure to replace the sticker over the access hole to keep the bugs out.
Keep a close eye on the tach and make it earn your trust before you "rev it on the red line". Actually if you are pushing your luck rpm wise you should be using a better quality tach anyway.
TRY THIS AT YOUR OWN RISK!
No guarantee but it worked for me!
Frank
Trying to keep the old stuff working.