how can i tell if my Tach is accurate?

[tigerfishes]

i have a 1977 Century I/O with a 190hp OMC. it has a 14 x 18p prop and when i talked with the prop guy about a 20p prop he said it didn't sound like the prop was the issue.
It seems like my Tach is not reading properly. short of just buying another, is there an easy way i can varify that it is or isn't reading properly?
I'm only doing 27-28 mph at 4600 rpms... and the temp is only running about 125 degrees. i can push it well beyond 6000 rpm( max of tach) and get up to about 37-38 mph. then the temp comes up to about 170. but i don't run it there long for fear of losing the engine.

 

[Bondo]

Re: how can i tell if my Tach is accurate?

Ayuh,... Compare it to a Shop Tach...

 

[tigerfishes]

Re: how can i tell if my Tach is accurate?

sorry for the stupid question.

 

[Doernuth]

Re: how can i tell if my Tach is accurate?

Is it the original tach? Some of the aftermarket ones have a switch on them for 4, 6 or 8 cylinder engines. Make sure the switch is in the proper position for your engine.

 

[picklenjim]

Re: how can i tell if my Tach is accurate?

If you can push it well beyond 6000 with that motor as you stated than I can assure you it is not accurate. You could check it with one of these http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html but all that will tell you is how far off it is. Just get a new tach.

 

[tigerfishes]

Re: how can i tell if my Tach is accurate?

it is an original. but that makes it about 33 years old. I was just looking at the set of gauges here on iboats the Tele's. are they a good brand? this is a decent boat that is semi project so these kinds of things are going to be getting replaced parts at a time. not looking for the best... just good ones that are priced fair that will work well. any sugestions?

thanks for the harbor freight lead...