How to ? Tachometer on sport jet

boerdoc1

Cadet
Joined
Jun 28, 2010
Messages
21
How do you hook up an automotive tach to a sport jet 90? Just for testing purposes, in a complete install. I want to set the idle speed and check the RPM at WOT.
 

Oode

Seaman Apprentice
Joined
Jul 13, 2010
Messages
41
Re: How to ? Tachometer on sport jet

Grey wire, at least on the XR120, goes all the way up the harness. I haven't figured out exactly which Tachs will work with it yet though... I would guess that a marine one would stand a better chance... Teleflex?? I've seen some at Overtons but they run about $60 and i'm not ready to shell out real money yet, but I'm about ready to slap an Oscilloscope on mine to check it out, but getting it running correctly has taken priority so far.... let us know what you try first..
 

espin

Recruit
Joined
Nov 15, 2010
Messages
1
Re: How to ? Tachometer on sport jet

I have a 94 SeaRayder f14 with the sportjet 90 in it. I have successfully replaces the nonworking speedometer with a working Tachometer. I ran a wire from the console back to the the boat side of the main harness connector where I found the grey wire. I had read that this was the tach wire so I hooked it up to my scope and I saw a very pretty 10v-0v square wave and the frequency varied with the rpms, so I felt pretty good about it. The first tach I bought was from a polaris ski mobile I think. It was a 3 pole which I assumed was what I needed since the sportjet 90 is a 3 cylinder. It registered something reasonable at idle but at higher RPMs it actually went down. Later it wouldn't register at all. I may have smoked it. It did fit well. Next I bought an actual sea ray tachometer that had adjustments for 4 6 10 and 12 poles. This time I chose 6 poles since there are 6 magnets on the flywheel. It registered a little high at idle, and maxed off the scale before I could get half way to WOT. It seemed like it was registering about 2x and maxed out the meter at 6k when I was turning 3K. I changed the poll setting to 12 just to cut it in half and it seems to work perfect now :) it fit in the speedometer hole well but I had to cut the bracket down for the thick mounting. I also felt like the meter trim was quite proud and stood out about 1/2 inch. Bothered at first but hardly notice anymore. $56 on Flea bay but it is working.
 

boerdoc1

Cadet
Joined
Jun 28, 2010
Messages
21
Re: How to ? Tachometer on sport jet

Thanks for the help. my boat is winterized up here in north Idaho but I will get one for next spring. I have found the grey wire but I did not know what speedo to use. Again, thanks
Kent
 

mables

Petty Officer 3rd Class
Joined
Sep 17, 2010
Messages
92
Re: How to ? Tachometer on sport jet

The main difference in this is something I just read and learned about myself, if it is a 4 stroke then an automotive will work but if it is 2 stroke some modifying to the internal resistors will be required. The reason being is that while a tach is a tach amd measures each time the engine fires a 4 cyclinder 4 stroke and 4cylinder 2 stroke do not fire the same amount per revolution a 4c4s will fire twice per revolution whereas a 4c2s will fire 8, also a reason for needing modification is that automotive tachs run off of when the distributor fires whereas boat tachs run off of the stator which is what was mentioned above. The poles should be double the number of cyclinders so 3cyl = 6 pole and so on. If you had a automotive tach on a 2c2s motor then it should theoritically work if you set the tach to read 8cyl automotive becase then it would be in the right pulse range to pickup 4 fires per revolution. There is an instructable about this and I can provide the link if needed, actually I'll go ahead and get it.

http://www.instructables.com/id/Automobile-Tachometer-on-an-outboard/
 

TeeBAG

Cadet
Joined
Jul 27, 2011
Messages
15
Re: How to ? Tachometer on sport jet

Is the grey wire you are referring to the one that comes off the rectifier? I'm trying to hook up a tach as well on a sport jet 90.
 

TeeBAG

Cadet
Joined
Jul 27, 2011
Messages
15
Re: How to ? Tachometer on sport jet

Thanks for the reply. Just wanted to make sure.
 

boerdoc1

Cadet
Joined
Jun 28, 2010
Messages
21
Re: How to ? Tachometer on sport jet

I picked up SeaRay tach on ebay and hooked it up and it works perfectly to the grey wire on the rectifier. It was switchable for 4, 6 10, 12 poles.
 

TeeBAG

Cadet
Joined
Jul 27, 2011
Messages
15
Re: How to ? Tachometer on sport jet

Thanks, that just what I wanted to hear.
 
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