3200rpm @ 52mph ?

[mirage2991]

By now I've read my manuals from cover to back, about 3 times, and I can't figure out how my tach on this Cobalt 190 is reading 3200 and speedo is indicating 52 mph. I have a 21 pitch prop on it. I would have thought that it would be more in the 4800rpm range (per the few prop/mph calculator I have tried on the net).
What could be the cause of the tach reading low? at idles it reads about 600rpms which is about where it needs to be...

any suggestions?

 

[Reel Poor]

Re: 3200rpm @ 52mph ?

Check the switch on the back of your tach. Make sure it's set to match you engine size.

 

[mirage2991]

Re: 3200rpm @ 52mph ?

good call, I wasn't aware that a stock tach would have that switch, but that would make sens since there's a V8 option for it...

 

[180shabah]

Re: 3200rpm @ 52mph ?

Even if it appears to be in the correct position, cycle it a time or to to make sure it is .

 

[Don S]

Re: 3200rpm @ 52mph ?

Get a shop tach or a timing light with a digital tach and verify your boat tach.

 

[HT32BSX115]

Re: 3200rpm @ 52mph ?

If you really want t o know where you stand with that stuff, not only do you need to ensure that your tach is correct but you must ensure your speedmeter is correct too. They are notoriously inaccurate. Check it with a GPS.

 

[QC]

Re: 3200rpm @ 52mph ?

Also check the speed with GPS. With either number being inaccurate it is just a waste of time trying to figure out . . . with both right, you can actually determine a thing or two.

Edit: Great minds . . . ^^^^^

 

[HT32BSX115]

Re: 3200rpm @ 52mph ?

Yeah....I type so slow usually everybody else beats me to the punch too!!

 

[mirage2991]

Re: 3200rpm @ 52mph ?

I'll do all that. when I looked under the dash I don't recall seeing a selector switch, but again, I wasn't really looking for it at the time. I'll check the grounds too.