Calibrating a new Tach

[Natesms]

I put a new tach in, it works fine, however I know the RPM's are off. There is an adjustment screw on the back to calibrate it, but I'm not sure what tool I can use to set it correctly. I looked for hand-held tachs and those cost more than the one I put on. Can I borrow something from an autoparts store? I'm not even exactly sure what tool to request.

I have a 1995 carbureted volvo 7.4 if that helps at all. Thanks

 

[saumon]

What model of tach did you get? Some are made for outboard and others for inboard.

The screw on the back isn't an adjustement screw, it's a selector switch and must be set according to the number of cylindres of your engine.

 

[Natesms]

What model of tach did you get? Some are made for outboard and others for inboard.

The screw on the back isn't an adjustement screw, it's a selector switch and must be set according to the number of cylindres of your engine.

Faria 33807 which said it is for I/O motors. There is an adjustment screw along with the cylinder selector on the back. It reads slow by a few hundred RPM.

 

[Splat]

Oh ok, I'll bite. .. how do you know it's off?

 

[Natesms]

Oh ok, I'll bite. .. how do you know it's off?

Good question. 2 things.

1. I can hear it (I did carb adjustments at the same time) and I set it to 600 RPM when not in gear and I can tell it's faster.
2. Even though it says I'm doing 500 rpm at idle I'm going much faster. Leaves a bit of a wake now and it didn't do that before. Not to mention the extra thunk when it goes into gear.

 

[saumon]

Faria 33807 which said it is for I/O motors. There is an adjustment screw along with the cylinder selector on the back. It reads slow by a few hundred RPM.

So is yours at the "3" setting (for 8 cylinders engines)?

 

[Natesms]

So is yours at the "3" setting (for 8 cylinders engines)?

Yes. I had to double check it because I had the selector stuck between 2 settings at one point and the needle would just go all the way over.

 

[Texasmark]

Well your shifting "thunk" is a sure enough clue.

 

[mrdancer]

You could try a sirometer (any good small engine repair shop should have one on hand). Otherwise, the small digital tachs are about as cheap as a sirometer, and probably easier for the general layperson to use and understand...

 

[no704]

Had an old dwell meter that had a tac setting. Don't know if ya could still find one?