tachometer related to voltage regulator

having trouble with tach readings, I purchased this used engine to put on the boat and wanted to see where I was reving at..purchased new faria tach and adusted the dial on the back as per manufactures guidline. The readings have been erratic. could the voltage regulator be the cause? I have checked the voltage on the battery and it reads 12:40...when I start the engine the voltage it reads 12:30...does this mean the regulator is fried.The battery is not a deep cycle.

Re: tachometer related to voltage regulator

big horn said:

having trouble with tach readings, I purchased this used engine to put on the boat and wanted to see where I was reving at..purchased new faria tach and adusted the dial on the back as per manufactures guidline. The readings have been erratic. could the voltage regulator be the cause? I have checked the voltage on the battery and it reads 12:40...when I start the engine the voltage it reads 12:30...does this mean the regulator is fried.The battery is not a deep cycle.

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It sounds like the regulator is bad,has to be the regulator,stator or battery.

Re: tachometer related to voltage regulator

What engine is this?

Re: tachometer related to voltage regulator

1990-1991 mercuy 40 hp 2 stroke 4 cylinder

Re: tachometer related to voltage regulator

12.6 is fully charged, and you're reading 12.3 with the engine running meaning you're not charging. It should be around 13-15 when running. If its original, that motor should have a rectifier and a regulator. From the sounds of things, the rectifier would be the first part I'd throw at it if I didn't have all the correct test equipment. The tach gets its signal at the rectifier not the regulator.They are a known point of failure. I doubt it's the stator. If you decide to replace it then get the CDI Electronics replacement which will combine the rectifier and regulator into one package and you won't need both. I can't remember off hand but I think the rectifier is now obsolete and no longer available. You might find one if you look hard enough.

Re: tachometer related to voltage regulator

Your engine could be either a single rectifier or single rect/regulator in one sealed contained unit and both are still available from factory. The rect/reg unit is used on 3 cylinder to V-6 engines and OEM# 815279T. Sierra makes a aftermarket 18-5743 that can be purchased here on iBoats. The single rectifier is 18-5707 and you can buy it here also...

Re: tachometer related to voltage regulator

Thanks for the info ...I will let you know how things work out