johnnyrude tach is over reading showing 4K at idle

greasemonkeyjmj

greasemonkeyjmj

Petty Officer 1st Class
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Jul 7, 2008
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264
i have a 73 johnson 50 horse that had a blown powerhead. the tach would read 2K at idle. on the water it seemed to read pretty close, the engine wouldnt turn up like it used to, but the tach was showing about 4300. well i replaced the powerhead with another one, now at idle it read 4k i havent had it on the water yet to see what it does.

thanks
 
metriccrescentwrench

metriccrescentwrench

Commander
Joined
Oct 22, 2007
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2,598
Re: johnnyrude tach is over reading showing 4K at idle

You need to make sure you've got the proper type of tach to work with your engine. On some tachs there will be a "poles" setting, that needs to be correct or you'll get a reading that is either too high or too low by a certain percent.

ALSO, many tach problems are actually due to a faulty rectifier.
 
greasemonkeyjmj

greasemonkeyjmj

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Re: johnnyrude tach is over reading showing 4K at idle

actualy last fall the tach was reading correct, and i havent changed it out, so we can rule out the wrongtack . and i thought about the rectifier, but i aqm not sure what the odds of 2 different one being faulty, but weird things happen
 
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82rude

Rear Admiral
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May 8, 2012
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Re: johnnyrude tach is over reading showing 4K at idle

2k at idle is way to high .i dont have that book handy but a 70 is around 700 -750 rpm at idle.
 
greasemonkeyjmj

greasemonkeyjmj

Petty Officer 1st Class
Joined
Jul 7, 2008
Messages
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Re: johnnyrude tach is over reading showing 4K at idle

it actually was showing about 750 at idle/ then it got to where it would show 2k at idle, now it shows 4k at idle, with a different powerhead and stator
 
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