Does anyone know the "pulse pattern" on the 400ex? I am trying to get a tach and need this info. This is the sparks per rpm the ignition produces.

 

I will try and take a stab at it.If you need to know the number of spark per rpm you can figure it out by saying the crankshaft spins 2 times for every spark produced.If you are running at lets say 3000 rpm then you are producing 750 sparks per minute (3000 divided by 4).But if the 400ex is the wasted spark motor(fires every rotation of the crankshaft) then your RPM and spark will be the same number I think.Somebody care to correct me on the wasted spark method?Good luck.

 

Paul: What brand of tach do you have on your recon? Did you mount yourself? Thanks!

 

I have the Tiny tach.You can buy it online at www.jackssmallengines.com for $39.95.It is too easy to install,all you do is wrap the wire around your spark plug wire and mount the unit wherever you wish.It gets it's power from the spark plug so you never have to worry about batteries.Good luck

 

Actually, most 4-strokes spark once every TWO revolutions of the crank. (Harley's spark every revolution being one of the exceptions, I'm not sure about the 400EX.) Therefore,if you are spinning at 3,000 rpm, you're sparking 1,500 per minute.
The "4 strokes" are 2 down and 2 up.

 

So once every TWO is the wasted spark system right?

 

Everyone i've talked to say that the 400ex and 300ex spark every revolution just like a 2 stroke does....which is a wasted spark system (on a 4 stroke) because you only need the spark every other rev, but it sparks every rev.

 

Yes that's right.
With a four stroke there are two crank revolutions per cycle. Intake and compression strokes on the first revolution, power and exhust on the second.
Most small engines fire on every revolution, and the "wasted spark" refers to the spark which is produced on the exhaust stroke, when there is nothing to ignite. The reason that it sparks is that there is no distributer, but a magneto on the crank, which creates a spark with every revolution.

 

Not exactly, guys!

PaulGP603, the 4-stroke engine doesn't "spin" "four times" for every essential spark pulse; it "spins" two complete revolutions for every complete cycle.

Newfiebullet, a "magneto" doesn't produce the "wasted" spark; the extra pulse comes from a projection on the alternator rotor that passes by the spark-triggereing magnetic pickup; the rotor turns with the crank; thus, the ignition system is triggered with every revolution.

And, trapperb1, while I haven't conducted a survey, I think most small four-stroke gasoline engines today use the "wasted spark" system, because most use the inductive pickup CDI ignition system, instead of the moldy-oldy points-and-capacitor ignition system. The older system usually had a point cam driven at half crank speed (like the valve camshaft), sparking every other revolution (the coil/points/capacitor circuit needed the "resting" revolution to build up the current for a healthy spark discharge).

Class dismissed. There WILL be a quiz!

Diogenes

 

teacher, may I ask a question ?
I wan to put a tiny tach from my shee to 3 cylinder machine knowing that the shee wastes 2 (like the strokes) -which would mean 4 for a 4 a stroke),how can I adapt it to my 3 cylinder that wastes sparks only on the left cylinder, if the right has already fired.
Thanks