K-17S How does it work

[SMITTY 23]

Okay had no start on my 417-A. Put a new set of points and a condenser started right up. Then I started thinking how does a twin cylinder run on 1 set of points and 1 coil with 2 wires. Do both cylinders fire at the same time or do they fire on both compression and exhaust on opposite turns. Anyone know.

Smitty

[WNYPCRepair 1,875]

From an article I read, they fire at the same time. There was something about a waste spark, but I forget what that part was. The cylinders are 180 opposed at the crankshaft, so both reach tdc at the same time


Someone with actual knowledge can probably explain it better

[boovuc 1,090]

Well......I have no knowledge at all on most things but............they really do fire at the same time. That's how they work! No distributor. No firing order. Most twin small engines fire this way.

[pfrederi 17,143]

They fire both at same time one is on the end of the exhaust stroke and does nothing..hence the term "Wasted"

[SMITTY 23]

Okay so if I read it right. Left cyl fires on compression stroke right cyl fires on exhaust stroke left fires on exhaust right fires on compression. Points break every revolution  plugs fire each revolution . The wasted spark is on the exhaust fires. Makes sense thanks for the replys







 

[WNYPCRepair 1,875]

My impression was they are both at compression and exhaust at the same time. So it fires both on compression, and a wasted spark on the exhaust stroke. Of course, I could be wrong

[boovuc 1,090]

I think the old B&S Opposed Engines fire one cyl at a time through the stroke process. (They fire opposite each other and that counters a lot of vibration).
Anyone with an old Shovelhead Harley will tell you about vibration and they vibrated because they fired at the same time. I only saw my speedometer when the motor was off! Come to think of it, I only saw my handlebars when the thing was not running!