Tach readings

TVZ · Dec 15, 2017

I have a cheap digital tachometer that I put on my 9N. I think the guy who wrote the instructions had about two years of English. You have to set the correct "mode". I tried "4P1R=4 spark per revolution",
figuring there are four spark plugs, cylinders, etc.. I'm getting a range of readings of about 400 at an idle to about 800 at full throttle. Does that sound like I have it set to the correct mode?

I see in my IT manual under governor setting that the correct speed wide open is 727 ? 800 PTO shaft rpm, 2000 ? 2200 engine rpm, or 1358 to 1494 belt pulley rpm. So if I am somehow measuring PTO shaft rpm,
it would be about right the way I have it set. Is that what I am measuring? Or should I really adjust it up to a max of 2000, since that is "engine rpm"? It seems like it's going pretty fast as is.

KL in Wi · Dec 15, 2017

Only two cylinders fire for each revolution.

Indiana Ken · Dec 15, 2017

Your [u:49a6e1ceaa]engine[/u:49a6e1ceaa] has 2 sparks per revolution. Each [u:49a6e1ceaa]cylinder[/u:49a6e1ceaa] sparks once per 2 revolutions. Now, where are you sensing the spark? Many of the small tachs use a wire wrapped around a spark plug wire to sense the spark. If this is what you have then: 1) placing the sense wire on any one of the wires going to a spark plug will communicate 1 spark per 2 revs to the tack. 2) placing the sense wire on the wire going from the coil to the distributor will communicate 2 sparks per rev to the tach. The tach will measure engine RPM in either case assuming the tach allows for the proper setting. You should read 400 - 500 RPM at idle and 2000 - 2200 RPM at full throttle.

Note - A N-9 (as built) has a front distributor which does not use a separate coil/distributor wire. Therefore, you will need to use the 1 spark per 2 rev setting unless the tractor has been modified in some manner.

Dell (WA) · Dec 15, 2017

TVZ........most rice-rocket digital tachometers are 12-volt and yer 9N was orginally 6-volt from the factory. Me? I'd use a 9-volt battery. It will also reduce yer weird non-stable readings. Just wrap yer sense wire around enny sparkie wire and set yer tacho fer 2-pulses per revolution. BTW, yer N-Engine MAX rpms shuld be 2200-rpms, idle speed, ennythang under 500-rpms is goot. I once got my eazy starting 6-volt 52-8N to idle at 375-rpms with a XSTR tacho. Remember yer carbie is BASS-ACKWARDS. OUT fer LEAN, IN fer ENRICH. Shuld bee about 1/8-1/4 turn. As fer the PTO shaft speed, that was important in early threshing machines, separating grain from chaff. Today, most N's are used fer brush-hogging and need the MANDANTORY ORC (over running coupler).......HTH, Dell, yer self-appointed sparkie-meister

TVZ · Dec 15, 2017

Dell, my tach uses a button battery in it. It's not connected to the tractor battery.

I have the sense wire on a spark plug wire. Wouldn't I want to set it at 2 revs per spark? Doesn't each plug fire every other rev?

THANKS

Tach readings

TVZ

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KL in Wi

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Indiana Ken

Well-known Member

Dell (WA)

Well-known Member

TVZ

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