Tach question

[Codeman96]

Ok guys here it goes I have a 1976 Merc 500 4cyl 50hp outboard, it has a switch box and 4 coils. Can an automotive tach be attached to this system and read correctly? The extra twist is that the tach that I have (why I am asking is because I already have it) also has a an induction lead on it that can clip on to the plug wire. Can I use this or just out of luck?

 

[pvanv]

Re: Tach question

Doubtful.
Yes, if it can be set for a 2-cyl 4-stroke car motor, it will read correctly with an inductive pickup.
Otherwise, it will read double the RPM's since you have a 2-stroke 4-cyl motor. Fires twice as often as the 4-stroke.

 

[Codeman96]

Re: Tach question

Actually it can So I suppose it should work. Thanks.

 

[coolguy147]

Re: Tach question

maybe to improvise u could possibly divide what u get from ur reading by 2 and there is ur rpm?

 

[sschefer]

Re: Tach question

There should be a switch on the back for 4/6/8 cyls. It should work. My test tach is from a junkyard mustang and it works on my Mariner 100 4cyl.

 

[Codeman96]

Re: Tach question

OK I am bringing this back up because I have another question to go with it. I can set the tach correctly (4cyl 2 stroke and I can set the tach to 2cyl 4stroke) question is can I hook it to the neg lead on the #1 coil for signal?

 

[sschefer]

Re: Tach question

OK I am bringing this back up because I have another question to go with it. I can set the tach correctly (4cyl 2 stroke and I can set the tach to 2cyl 4stroke) question is can I hook it to the neg lead on the #1 coil for signal?

Not sure, depends on the engine. The rule of thumb is to take it from the trigger coil that lives under the stator or from the rectifier. Of the ones I've done, the trigger wire is normally yellow and the rectifier signal wire is normally gray.