Kill switch/coasting

[charlie55]

I've noticed that the function of the kill switch seems to differ somewhat depending upon when you're shutting down:

1) In "normal" circumstances where you've come to a complete stop, the kill switch shuts the engine off immediately.

2) In situations where you're, let's say coasting to a rolling stop, the engine doesn't cut out until your speed or RPMs hit a low threshold point. I haven't recorded the exact point at which this occurs, but it's not as if the tranny and clutch are locked up and still "driving" the engine. Rather, the engine is indeed running.

Are there some "smarts" in the CDI that try to delay engine shutdown until some assumed point at which the clutch would theoretically release?

Not a problem mind you, just curious.

Thanks

[illnoise]

Good question. I always figured the engine's inertia just kept it running for a while, but I guess that wouldn't work on a bike with an on/off killswitch (as opposed to the push-button killswitch on vintage bikes) because it would permanently cut power to the plug.

Is it dieseling, maybe? Could the compression be igniting the fuel?

I guess it could be a safety feature, but I think most bikes do it, even more primitive ones. We used to ride by friends on P200s and flip their killswitches at 50mph in gear, and it didn't (usually) throw them off the bike.

Wow, I haven't thought to do that in a while. I used to be a jacka**. Maybe it's time to bring that practical joke back.

[Lostmycage]

I've noticed the same thing. The engine will die when it returns to idle (when the clutch disengages). I'm not sure how the kill switch works, since it seems that it'll keep running the engine as long as it's engaged. What seems to happen is that as long as the rear wheel spins the clutch (therefore spinning the crankshaft) it'll keep the engine turning.

I would have thought that the kill switch would cut power to the CDI, but I'm guessing that to keep the bike from locking up and causing a spill, there's a precaution set in to let the engine idle down then die.

It is kinda weird though. One thing I haven't tried is applying the throttle while the engine's running with the switch set to kill.

[BGK]

The kill switch stops the spark. There is no spark after the kill switch is turned off. The engine isn't technically running. The clutch is still engaged because the whole motor/transmission/rear wheel is still moving at the same speed it was just before you hit the switch. At this point the rear wheel is giving the power to spin the crank shaft rather than expanding gas from rapidly oxidizing fuel. So they will happily spin together until the crank shaft slows down enough for the clutch to disengage. The motor will still sound like it's running because it's still pumping air just as it would when running but it's just not being pushed by an explosion during one of the two superfluous strokes of the Blur motor. If an engine is hot and you cut spark it may still run-on a bit but not for very long unless it's really hot (like broken hot)

[Lostmycage]

That sounds like what I would have figured in my head (but couldn't put in words, hehe). Good post BGK. Thank you.

[charlie55]

Thanks for the explanation. Makes complete sense.

[illnoise]

Brooke, you're hilarious. I think your joke went over everyone's heads. : )

Bb.