I was thinking about this the other day and could not remember which way it goes.......    ???

It fires even on the dead stroke which contributes to burning unburned mixture in the exhaust (popping). To keep it simple the ignition and alt/generator coil are combined and fires on each revolution of the crank. So if you buy a tachometer make sure you're getting one that works on a 2 stroke even though it's a 4 stroke

I had made that mistake when I bought a small induction tach. I bought a 4 cycle version, which is correct mechanically, but I needed the 2 cycle version electrically. Once I made the switch, the tach works great.

So......the interesting subject of what is single fire and what is dual.    Usually dual fire bikes have more than one cylinder!! Also, Two wires out of one ign coil is a big clue.   In reality,  today's manufacturers do funny things with ignitions especially with electronic ign's and you need to find which tachs work on the bike.   Don't try the "well if it's a ........" and 2-cycle and 4-cycle dosen't mean dual fire or single fire,  but mostly 2 cycles are single fire.

So...here you go....

I have a MMB Electronic Tach on mine that is a 1:1 tach and it works nice.   It did NOT work on my old bike which was a '82 Honda CM250C Custom (TwinStar engine) which is considered 100% a dual fire bike ((it gave twice the real RPM on the Honda)).

So, since my tach didn't run on a dual fire bike and runs nice on the LS650, I would say LS650's need single fire tachs.

Second,  since there are many threads on the mini digital tachs that work, and from hunting for a tach for the Honda, I found that they're single fire because they are made for lawn tractors/mowers, again I would say LS650's need single fire tachs.

Lastly, occasionaly you will see an EBay seller listing a mini analog tach for the LS650,  that is also same tach that is sold for single fire HD's.......need I say more....

Note: Need to attach the electronic tach's (not induction)to the B/Y (black/ yellow strip? ? ?) wire on Ign coil not the O /W (orange / white stripe? ? ?) wire.  I know from learning from an OOPS.....

To add to Kropatchek, it is called "Wasted Spark".  It fires on both strokes at TDC.

Much simpler to do the ignition with a pick up coil on the crankshaft than timing off the cam shaft.  The extra spark on the exhaust stroke is supposedly good for removing small amounts of unburned gas, too.

I remember that "back in the day", a tach came with clips or jumpers that allowed you to set the number of cylinders...of course, that was on single coil (point) ignition systems.

Anyway...isn't the tach counting revolutions and not compression strokes?  If there is one pulse per revolution, it is a no brainer for the tach.  1=1.

So yeah, at 1100 RPMs we would be running at 550 CPMs (compressions per minute).

Suck, Squeeze, Bang, Blow...that's it

I keep thinking of my old 250 Honda (same engine as the 250 Rebels have now).  Two cylinders, 180 deg out (one compressing, one exhausting at same time)

T-Mack, if your Honda was a 180° twin, it worked "one compressing, one banging".

When one goes up, the other goes down.

If both went up&down at the same time, you had a 360° twin.