accurate tach?

[vesselgreenhead]

Is there an easy way to tell if a new tach is reading correct without having to install another. It seems to be wrong to me because i'm on the 3rd prop, dropping from 21, to now 17 pitch on a 150 mercury saltwater carb. on a 18 foot commercial heavy guage aluminum boat. Also frustrating to go from 51mph to 43mph per GPS and still only turn 4900 rpm's. Motor is mounted correctly. Prop is mirage plus "expensive" and i'm trying to keep from going to the dealer. Appointments are a pain to get. any easy suggestions? everyone i talk to is getting between 5500-5700 rpm's on similiar boats and motors where i'm from just as my manuel suggests. suggestions please FYI-factory Merc. Tach.

 

[Hooty]

Re: accurate tach?

The only way I know to verify a tach is with another tach,like a strob or hand held manual tach.<br /><br />c/6<br /><br />Hooty

 

[norman158]

Re: accurate tach?

take your local mower mechanic out for a ride and ask him to bring his old vibro tach along these are pretty accurate in the right hands