Spark plug firing per revoultion??

[mocktar400]

How often does the spark plug fire per revoulution?

Want to install a digital tach and need to program

the unit to 1. spark plug fires twice per revoulution, 2.

spark plug fires once per revoultion, or spark plug fires

every other revolution. ?

Thanks.

[psych_ward]

1-stoke brings in fuel air 2-then return stroke compressess mixture at or very near top dead center spark plug sparks once 3-and sents piston on power stroke then 4-return exhausts and 1-repeat. So I am only best guessing but it is probably only 1. Hope that helps. ?

[DFXXX]

I'd try setting it at 1, and if you are getting some ridiculous RPM like "6" or "18,543,123" then you know something wrong. Nothing going to get hurt if the tach is not adjusted correctly the first time. ?

[mocktar400]

Thanks guys, will give it a try. :worthy:Am excited to see if it really works. It has an hour meter function too.

[10guy]

It's a four stroke, the plug fires every fourth stroke or once every other revolution. A two stroke fires every revolution.

[Wayward Son]

it fires a wasted spark.

fires once every revolution.

[tom slick]

as burned mentioned, i'll clarify a bit. it fires on compression and on the exhaust stroke. the exhaust stroke is "wasted".

[10guy]

Why do they do it that way?

[NateTheGreat]

Well I will take a stab at it and say its a combination of 2 things.

1. By firing on the exhaust gases you may burn off some residuals and create a cleaner emmision bike....

But more likely is...

2. Its probably cheaper and easier from a design standpoint to make a CDI system / stator etc that sparks every revolution. ?

[tom slick]

Why do they do it that way?

simply because the magnet on the flywheel passes by sensor each revolution of the crank. 2 revolutions of the crank = once complete cycle on a 4 stroke, the compresson and exhaust strokes are opposite each other and there is nothing to lose/gain from it firing on the exhaust.

to fire only on the compression stroke you'd have to have the sensor on the cam, that would make the head assembly much more complex and bulky then it already is.

most cars and multi cyl bikes now use "waste spark" ignition systems, that's why you have one coil for 2 cyls, and the cyls are opposite each other in the firing order.

[Wayward Son]

motorcycles have been that way for 30+ years.not all,but most.

[mocktar400]

? :cry: Got it hooked up but no workie.

May not have a good ground, try again tonight. You guys

are great. Thank you. ?

[MutualBill]

No wonder they are so prone to popping on decel when the bike is fat.

[AndrewQ]

Waste spark has no effect on decel backfires ?

[psych_ward]

that wasa good info and I didn't know it fired every time ? :cry: ?