Pole setting for tach

[CBC]

I have a 1978 Merc 800 4 cylinder 2 stroke I just put in the water and the tach (Airguide) seems to be reading twice the real RPM's (like 8000 RPM'S at 3/4 throttle?!!!) The boat really scoots and didn't blowup after an hour of testing so I'm pretty sure the pole setting isn't correct for that motor.

Can anyone give me a "how to" on that tach and motor combo?.... the tach is original in a 1976 Larson.

Thanx,
Crunch

 

[Barnacle_Bill]

Re: Pole setting for tach

It should be set to 6P (pulses)

 

[JoeCrow]

Re: Pole setting for tach

I may be wrong but I think that's a 12 pole motor
What setting are you on and what settings are available?
If it says 4-6-8 that may be cylinders, not poles, and it probably won't work correctly

 

[CBC]

Re: Pole setting for tach

Thanx for the reply Joe.... I've been running through all the posts I found by searching and ran across a chart that says you are right about the number of poles, it also says that I set it on 6P.

Thing is, there is no adjustment screw on the back! I took the tach apart last evening and on the circuit board there is a round thing with a plastic do-dad with a slot that looks like it's meant for a screw driver... it was too dark to see if there was any writing on the thing but I'm suspecting that there might be

Hopefully someone that is familiar with the old Airguides will tell me if that is what I'm looking for.

Thanx again,
Crunch

 

[Silvertip]

Re: Pole setting for tach

A 12 "pole" stator produces 6 "pulses" so you need to be sure what the tach settings actually represent.

 

[JoeCrow]

Re: Pole setting for tach

I checked, it is a 12 pole motor and it does produce 6 pulses as Silvertip said
The plastic thing with a slot for a flathead screwdriver sounds like the setting adjustment,
Just be careful as I said....
If it says 4-6-8 it may be a setting for cylinders, not poles

 

[CBC]

Re: Pole setting for tach

Thanx all.... as soon as I get off work I'll get a magnifying glass and have a look at it.

Crunch