How to set up an induction tachometer

[kalebsheridan]

Hey everyone, so I got one of those cheap induction tachometers to use for tuning my outboards, the ones with the long wire you wrap around a sparkplug wire. I set it up on a Honda kicker and it seems to work well. When I set it up on my 50hp Force, I seems to get 1600 Rpm at idle. Did I set this up correctly? How many pulses per revolution should this motor be doing? Do any of you guys have experience with these induction tachs? Any help would be awesome

 

[topgun3690]

I just got one to check my main tach.....I have a 3 cylinder so I set it at 3 spark per rev setting.....seems to work well. Try setting it at 2 spark per rev for your 2 cylinder and see it that works better......

 

[kalebsheridan]

Okay cool I think that is what I tried. I mean my motor could be idling at 1600 rpms. When I tried to reduce the idle for tuning, I could not get it down below 900 however. Granted I'm chasing a misfire so that could be why, but I don't know if I can trust my tach. How many wraps do you do?

 

[topgun3690]

How many wraps do you do?

The one I bought off ebay said at least 5 wraps....and connect the ground wire to a good ground.

 

[kalebsheridan]

Okay mine has no ground. Just one long wire.

 

[topgun3690]

Okay mine has no ground. Just one long wire.

This is the one I bought....that silver C connector is for the ground.....

 

[Jiggz]

Hey everyone, so I got one of those cheap induction tachometers to use for tuning my outboards, the ones with the long wire you wrap around a sparkplug wire. I set it up on a Honda kicker and it seems to work well. When I set it up on my 50hp Force, I seems to get 1600 Rpm at idle. Did I set this up correctly? How many pulses per revolution should this motor be doing? Do any of you guys have experience with these induction tachs? Any help would be awesome

It looks like it is set correctly. The type of tach you have actually relies on the spark plug getting energized. And with this Force motors, they have what is called dual spark meaning you get two sparks per revolution in each cylinder. So the tach reads twice the actual rpm. In a non-dual spark 2 cycle motor, you get one spark per revolution of the crankshaft. In a 4 cycle motor you get 1 spark per two revs. But in a dual spark 2 cycle motor like Force you get 2 sparks per rev. Note a second spark on the plug while the piston is at BDC would not ignite the fuel oil mixture.

 

[kalebsheridan]

This is the one I bought....that silver C connector is for the ground.....View attachment 389787

Ooh I see. Maybe the next one I get will be that one if the mighty TopGun likes it. How long is the cord? Would like mount one on my dash.

 

[kalebsheridan]

It looks like it is set correctly. The type of tach you have actually relies on the spark plug getting energized. And with this Force motors, they have what is called dual spark meaning you get two sparks per revolution in each cylinder. So the tach reads twice the actual rpm. In a non-dual spark 2 cycle motor, you get one spark per revolution of the crankshaft. In a 4 cycle motor you get 1 spark per two revs. But in a dual spark 2 cycle motor like Force you get 2 sparks per rev. Note a second spark on the plug while the piston is at BDC would not ignite the fuel oil mixture

Okay so each revolution there are two sparks from each plug, one dry spark and one igniting spark? You think my tach was reading double then? As in my motor was doing 800 at idle, but my tach was reading 1600 pulses?

 

[Jiggz]

Okay so each revolution there are two sparks from each plug, one dry spark and one igniting spark? You think my tach was reading double then? As in my motor was doing 800 at idle, but my tach was reading 1600 pulses?

That is correct. You just have to bear that in mind and divide the rpm indicated by two. I have the same tach you have and tried everything until I came across a page explaining the dual spark system on most 2 cycle engines.

 

[kalebsheridan]

Okay well that's really good to know then. I though my motor was idling super bad, but sounds like I was setting the idle speed way too low. Still has a miss but not as bad as I probably feared. I guess a tool is only as good as the person using it lol!

 

[kalebsheridan]

Hey so since I touched the idle speed screw, does that mean I need to buy a timing light and reset or check the timing? Or can I just adjust the screw until I get 750 rpm in gear?

 

[Nordin]

If you mean idle screw by the one at the timing tower which rest at the block you do not need to reset or check the timing after you touched it..
If you change the trigger ring and you have to fiddle with the rod that moves the timing plate and is connected to the timing tower, then you have to check the timing.

 

[topgun3690]

How long is the cord? Would like mount one on my dash.

It wasn't long enough to reach my dash......way too short. Might be able to splice in some wire to make it longer but didn't want to do that.

 

[kalebsheridan]

Okay cool thanks Nordin, no I did not touch the timing rod. I did replace my trigger recently, but I kept the timing rod at the same length the original one had.