erractic tachometer reading

I've got a pair of 2004 BF 150's. The tach's have never worked perfectly for the year that I've owned the boat. I've been meaning to replace them, but they've worked just well enough that I haven't gotten around to it. They both read erratically and occasionally for no apparent reason they will start to swing high for no reason. If I tap them, they will settle back to where they belong. My flow scan is what I've been using to keep things in synch.

Is this a common problem as tach's age? I'm guessing its not a wiring issue, but looking for a second opinion.

Thanks in advance,

'Slot

There could be several reasons for erratic tach's. The most common is a bad contact on the setting screw in the back of the tach.

Get to the back of the tach and you will see a very small screw that rotates to several different settings. See where it is set now, then take a small screwdriver and rotate the screw back and forth several times. That, by itself, may clean up the contacts and settle things down.

Mike

Excellent advice. I'll check that out as soon as I get a chance and report back my success, or lack there of

Many thanks,

As promised, this is a follow up.

Turning the adjusting screw back and forth did work to stabilize the tach readings. Very happy with that part. It looks like I'll ultimately replace them anyway as they are about 300 rpm's apart at cruise. If I synch by the tachs, they don't sounds just right and they are 2gph apart on my flow scans. If I sync by my flow scans they sound just right.

Thanks,

'Slot

Good! Just double check to be sure that both tachs are set to the same setting.

Mike

A little fix for some tachos when behaving strangely is to put a 1K resister between the sender wire and ground wire behind the tacho. Obviously it doesn't always work but it's a cheap and easy test. Honda actually even makes a resister pack for this purpose on some outboards which effectively does the same thing.