tach question for you

lonemust

Petty Officer 1st Class
Joined
Apr 2, 2009
Messages
205
Ok.. I'm beginning to think the tach that was in my boat is reading wrong.. I have another tach which i just put in Saturday.. I have a Starcraft V180 running a 140 merc w/mc-1 outdrive. this is a fiberglass hull.. Now the tach that was in the boat when i got it last year and just took out yesterday, had 2 wires( 1 wire from the coil and 1 wire from ignition switch) this as far as I know is the factory tach for the boat. Now the tach I put in in its place only has the the wire from the coil going to it.. before I switched the tachs the boat ran ok but just seemed to not run quite like it should.. after hooking up the single wire tach, started up the engine and it sounded like it was running better then with the 2 wire tach.. could it be something is wrong with the 2 wire tach. and what is the advantage of a 1 wire tach over a 2 wire tach or vise versa?? O before some asks the "new" tach came out of a dashpanel exactly like the one in my boat except it is a 1wire instead of a 2wire tach, everything else was the same and the whole thing would bolt right in with no problems..
 

Doernuth

Petty Officer 1st Class
Joined
Jul 6, 2010
Messages
332
Re: tach question for you

Usually there is one wire for the tach and one wire for the light in the tach.

Does your new guage light up?
 

lonemust

Petty Officer 1st Class
Joined
Apr 2, 2009
Messages
205
Re: tach question for you

yes the "new" tach has a light. the wire for it is ran to the pos terminal for the oil guage.. the tach i took out had to have a pos wire or else it wouldnt work.. thats what has me puzzled.. the "new' one does not have a terminal for the light or a pos wire..
 

lonemust

Petty Officer 1st Class
Joined
Apr 2, 2009
Messages
205
Re: tach question for you

ok an update here.. took the fish boating today.. lol the boat fishing today.. the tach I put in on saturday showed me running on average 4400 rpm at wot. 200rmp shy of max. I have a 14.5x23 alum prop. so thats about right. fish finder showed me running 42.8 mph and my airguage speedo showed 36mph. i think the fish finder is more accurate. So I think my "old" tach is off by a few hundred rpm. it showed me only running 3900rpm on friday.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,082
Re: tach question for you

So I think my "old" tach is off by a few hundred rpm.

Ayuh,... I'm bettin' yer Absolutely Right,....
 
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