Odd Tachometer Problems!!!

[Bryan Sumrell]

I am in the process of restoring a 1974 15' Thunderbird tri-hull, I originally tried a 1998 50hp Evinrude and did not like the performance and have now installed a 1974 70 hp Johnson. With both of these motors and with 2 different tachs they do not act right. With both motors the tach will get to around 4,000 and fall back and then act erratic. If you run up to 4,000 and hold the tach will stay for a little while. 2 different motors and 2 different tachometers same problem. The 70 will be permanent and would really like to get the tach working properly. Thanks, Bryan

 

[emdsapmgr]

Re: Odd Tachometer Problems!!!

An odd situation, for sure. You've swapped both engines and both tachs-same problem. If it's not the tach, usually it's the rectifier which is bad. Unusual to have exact/same symptoms with two different engine/tach setups. You might confirm that the tach lead (gray wire) from the engine to the control box/tach has continuity-does not short to ground somewhere in the wire harness. I had to run a replacement tach wire from the engine to the box on one of my engines when it just went dead-probably either an open or short to ground. That took care of it.

 

[Bryan Sumrell]

Re: Odd Tachometer Problems!!!

Yes sir I've run a wire from my new adapter harness straight to the tach, still no luck. I may run from the engine all the way to the tach and see if that helps. Thanks for you help.

 

[boobie]

Re: Odd Tachometer Problems!!!

Have you got the tach set on position # 6 ??

 

[Bryan Sumrell]

Re: Odd Tachometer Problems!!!

No it's been on 4 on both tachs for both engines at the recommendation of a coworker. I just switched it to #6. Will this solve the problem? Thanks so much for your advice.

 

[Bryan Sumrell]

Re: Odd Tachometer Problems!!!

Just to point out and after further research both of these tachs are Faria and apparently their settings are a little different. Have it set on 6 now, hopefully this helps. Trying to prop a boat with an erratic tachometer is not fun lol.

 

[boobie]

Re: Odd Tachometer Problems!!!

Let us know the out come.

 

[emdsapmgr]

Re: Odd Tachometer Problems!!!

Most all marine tachs use the same setting numbers. 6 should be the correct one for your engine.

 

[Bullrider]

Re: Odd Tachometer Problems!!!

opcorn:

 

[DavidD]

Re: Odd Tachometer Problems!!!

My Tach has no adjustable setting and it came off a boat with a 4cyl and I put it on a 2 cyl. Would it be accurate with a 4 to 2cyl swap?

 

[emdsapmgr]

Re: Odd Tachometer Problems!!!

Hard to say. Marine tachs count pulses from the alternator (charging system) on outboards. They vary somewhat, base on type of engine, that's why most modern day marine tachs have an adjustable switch on the back that can be set to correctly count the alternator pulses for that specific manufacturer.