Two Stroke Wasted Spark

[boscoe99]

I never thought about a two stroke using a wasted spark ignition system. Did not make sense to me since the plug needs to fire every time the piston is at top dead center because the two stroke fires every time the piston is there. Well apparently there are two stroke ignition systems using one coil to fire both plugs at the same time. One cylinder when at top dead center and one at bottom dead center. Seems like fuel/air would be coming into the cylinder when the piston is at BDC but maybe it won't light because there is no compression????

It was used in the early 25 HP two cylinder two strokes. Later 25 HP two cylinder models use two ignition coils and two pulser coils, one for each ignition coil. See below. Learning is a never ending process.

Rodnut, do I have this right?

[99yam40]

I would think that at BDC there would still be burnt exhaust gases heading out the exhaust port so the spark does not hurt anything.
it would not suck any new fuel/air charge back in until the pressure is dissipated.
Just my thoughts

[boscoe99]

The piston going down is compressing the fuel/air mix within the crank case. When the piston gets down to the point that the intake port opens fuel/air starts flowing in. Why it does not light up is not known to me.

[99yam40]

Could it be that there still is enough pressure from the exhaust gases to keep it from flowing in until the pressure dissipates/equalizes?
always heard that as the exhaust leaves it sucks some in from the intake

[Jason2tpa]

I don't have anything valuable to add, but i do wonder how boscoe always gets a hold of the sweetest schematics. He's got a treasure trove of these.

[panasonic]

I never thought about a two stroke using a wasted spark ignition system. Did not make sense to me since the plug needs to fire every time the piston is at top dead center because the two stroke fires every time the piston is there. Well apparently there are two stroke ignition systems using one coil to fire both plugs at the same time. One cylinder when at top dead center and one at bottom dead center. Seems like fuel/air would be coming into the cylinder when the piston is at BDC but maybe it won't light because there is no compression????

It was used in the early 25 HP two cylinder two strokes. Later 25 HP two cylinder models use two ignition coils and two pulser coils, one for each ignition coil. See below. Learning is a never ending process.

Rodnut, do I have this right?

Yes sir you do have it right.

There are many two stroke twin cylinder engines that use a "waste spark" system. This is not only for four stroke engines.

I had several twin cylinder two stroke snowmobiles that used this system (it is widely used in snowmobiles), the Yamaha RZ350 twin cylinder motorcycle uses this system, and I believe the Yamaha 4 wheeler "Banshee" twin two stroke also uses a waste spark system.

I also have a 1977 Kawasaki KZ 1000 FOUR STROKE motorcycle that uses the waste spark system. Two coils for four cylinders. (but we all know that)

I am pretty sure that the old mid eighties Yamaha enduro twins (at least the small ones 25hp) had a waste spark ignition. Could be wrong though.

[rodbolt17]

lots of small motors and some large motors use a waste spark system.
if you don't compress the mix it wont light.
biggest motor I have seen with waste spark is the F225.

[boscoe99]

Yes sir you do have it right.

There are many two stroke twin cylinder engines that use a "waste spark" system. This is not only for four stroke engines.

I had several twin cylinder two stroke snowmobiles that used this system (it is widely used in snowmobiles), the Yamaha RZ350 twin cylinder motorcycle uses this system, and I believe the Yamaha 4 wheeler "Banshee" twin two stroke also uses a waste spark system.

I also have a 1977 Kawasaki KZ 1000 FOUR STROKE motorcycle that uses the waste spark system. Two coils for four cylinders. (but we all know that)

I am pretty sure that the old mid eighties Yamaha enduro twins (at least the small ones 25hp) had a waste spark ignition. Could be wrong though.

Please refrain from commenting to/on my posts.

[TownsendsFJR1300]

Seems Boscoe needs to cough up that "tasty crow" I procured....

I forgot re my old 1975 Yamaha RD 350 twin 2 stroke. The crankshaft was offset 180 degrees, Ie, each cylinder, power stroke, fired when the other piston was at THE BOTTOM of it's stroke, on a multi-cylinder two stroke..

I was reminded by another members post:

"There are many two stroke twin cylinder engines that use a "waste spark" system.

I had several twin cylinder two stroke snowmobiles that used this system (it is widely used in snowmobiles), the Yamaha RZ350 twin cylinder motorcycle uses this system

[boscoe99]

https://en.wikipedia.org/wiki/Eating_crow

[rodbolt17]

I find my crow tasty with Bush Ice or Evan Williams with a splash of fireball.
everybody gets it occasionally.
I had almost forgotten almost all the twin cyl small yamaha's used a waste spark at one time or another.

[TownsendsFJR1300]

I find my crow tasty with Bush Ice or Evan Williams with a splash of fireball.
everybody gets it occasionally.
I had almost forgotten almost all the twin cyl small yamaha's used a waste spark at one time or another.

Yep, NOT the first WASTE spark for a two stroke...

Does crow taste like chicken??


I suspect time to MOVE on....Something learned....

[rodbolt17]

dunno.
usually the reason I am eating it is because I started with the Bush or the Williams first .