Tachometer is wrong thank god

krisnowicki

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In an old post I was asking about my outdrive ratio. I have the 5.0 package gen II below in my sig.
I and others thought it was a 1.5 SO I was doing rpm speed prop and slip calculations on the rbbi website as a 1.5

With my tach it was saying I was getting 3800 rpms on a 21p at 44-46 mph gps which left me with about .13 or .14 slip . Since I know the speed is right and I now know the ratio is 1.64 at 45 mph and with a slip of 10 percent which is really low I would be at 4200 or with .15 which is more likley I am at 4366.

So I am missing 4-6 hundred with a 21p
This would also explain why whenI put my 19 on I get up to 38-3900 and thats it . I was so worried because at 3800 I was lugging the engine so bad and didnt want to harm it.

Question is . Is it the tach or wire? All the connections look good and clean?
 

Don S

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Re: Tachometer is wrong thank god

Run a temporary wire from the coil - terminal, to the gray wire terminal on the tach. And run it and see. If it's the same, replace the tach.
 

krisnowicki

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Re: Tachometer is wrong thank god

thanks dons just like a jumper wire with alligator clips?
 

Don S

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Re: Tachometer is wrong thank god

Just a long wire with ring terminals on each end. Hook one to the coil - terminal and the other to the tach. (remove the harness wire from the tach.)
 

krisnowicki

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Re: Tachometer is wrong thank god

Don S. at 4200-4350 would this be ok? from what i read the WOT range is 42-4600 is this low part of the range fine or should I keep th pitch down to keep it closer to 4500-4600?
 

Bondo

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Re: Tachometer is wrong thank god

at 4200-4350 would this be ok? from what i read the WOT range is 42-4600 is this low part of the range fine or should I keep th pitch down to keep it closer to 4500-4600?

Ayuh,...

That'll be Fine for general boating,+ cruising,..
But,...
You'll probably want the next lower pitch for any sking or tubing...
 

krisnowicki

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Re: Tachometer is wrong thank god

Ayuh,...

That'll be Fine for general boating,+ cruising,..
But,...
You'll probably want the next lower pitch for any sking or tubing...

Awesome I got a 21- laser II for crusing and a 19p with a slight cup ss for tubing thanks guys
 
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