Two questions - what tach to use and just got huge commercial battery

[WA-Newb]

Tinkering with a few things on my boat and I am getting to the point where I need to have a tach for adjustments etc.

I have an old dwell / tach for autos...I am pretty sure this won't work but if anyone knows a way I am all ears.
I also have an auto tach that I got for a couple bucks but have never really looked at it since buying it (planned on putting it in old chevy truck).

I do not have any extra money to throw around so everything I need to do has to be as "ghetto" (cheap) as possible..lol
Sorry for the term but until I get this motor running decently every dollar bill spent is money down the drain.
Once I have it running decent then I can start putting a little money into her.

Anyway to adjust the timing, carbs...whatever else that I may need to do I am reading I need a Tach.
I don't even know how to hook one up yet but the first thing is figuring out what to buy / look for.

The motor is a 1968 Evinrude Starflite 100hp...has a power pack and electronic ignition (I don't know answers to points distributors etc....still learning)

So first question...
What is the cheapest way to use a tach on this motor...can be mounted or test kit...whichever.

Next question...
The boat needed a battery when I got it and I have been using my old chevy trucks battery...but I just found a huge commercial battery that I bought for $20...it appears to be out of a tractor or heavy piece of equipment. shows full charge and is 12 volt.
Can I use this type of battery for this outboard (or any outboard)?

Thank you.

 

[Silvertip]

Re: Two questions - what tach to use and just got huge commercial battery

Auto tachometers and tachometers for a two stroke magneto ignition are different in how they count engine revs. Your outboard counts pulses from the charging system. This is typically six pulses/revolution. The auto tach is generally set up to read "ignition" pulses from either a 4, 6, or 8 cylinder engine. A four banger produces 2 pulses per engine rev, a six cylinder does 3 and an 8 cylinder does 4 pulses per rev. So there is the issue -- setting the tach for a six cylinder engine (3 pulses) would cause the tach to read 1/2 the actually rpm on your boat. That is IF the tach can recognize the differences in the pulse waveforms. A 12 volt battery is a 12 volt battery. It can be the size of match book or the size of a dump truck. Your engine won't care.

 

[WA-Newb]

Re: Two questions - what tach to use and just got huge commercial battery

Thank you for the reply...I am having some bad problems now with my motor after "fixing" some wires and installing that new battery so I guess a Tach is least of my worries...sigh

I am reading here and there that some power packs don't have tach outputs either...since I cannot sind my power pack model anywhere I don't know if I can even hook up a tach or not...yet another sigh...lol

Thanks again thouhg..I will revisit your reply when (or if) I get my motor running again.

 

[NYBo]

Re: Two questions - what tach to use and just got huge commercial battery

The tach feed will be from the stator, not the power packs.