Safety post: Engine starts too easily

General Discussion
1

Sort of the opposite of most starting problems. Something very unusual happened to me the other day when starting my lawnmower, think it is worthwhile to share for safety sakes. Cold start, often requires several pulls. Cold day, cold engine, so before pulling decided to remove air filter & spray a dose of starter spray into intake. After I did this, I remembered a comment by @Bing saying he positions the engine rotation so intake valve is open before spraying. So I pulled the rope ever, ever so slowly to get engine into that position. Almost impossible to have pulled more slowly. rrr r rr rrr … without warning, engine starts and runs … lol …

Bottom line: Be very cautious. Gasoline engines can start without warning with a bare minimum of rotation speed. Anybody else ever had this happen? Either small engine or car engine? Maybe this sort of thing can only occur with starter spray?

2

That’s for chain saws. Bring it up to a compression stroke, then a good yank.

3

I know someone with a BMW R60. He could some times get it to start without being kicked by just moving the spark advance.

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4

In any situation where this would be dangerous, the spark plug wire should be pulled first, of course.

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5

Great idea if you don’t want it to start.

Except that for all purposes @George_San_Jose1 was trying to start the motor. Which won’t happen if you disconnect the spark plug wire. In this case it started sooner and with much less effort than usual.

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6

This was not an engine problem , this was an operator malfunction.

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7

But particularly when highly volatile aerosols are sprayed into the intake beforehand :wink:

My Stihl chainsaw has an interesting feature that I don’t particularly like for this reason. When pulling the starting rope, you’re winding a spring that will let loose when the appropriate tension is achieved and turn over the engine. It requires a different approach and care because if you treat it like an older design and just start pulling, it can start during the retraction of the cord when you least expect it. Most full length pulls will achieve the required spring tension but shorter pulls many times do not. Supposed to make it easier to start but caught me off guard a couple times when I first got it…

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8

I’ve heard warnings before that a lawn mower engine can start unexpectedly. It appears those warnings are valid. I concur, especially for cold engine, that the starter fluid sprayed into intake probably played a role. Still, I’m wondering how a large enough voltage ever got generated by the dynamo to fire a spark plug, given the slow crankshaft rotation. My guess is at the end of a compression stroke there was enough compressed air in the cylinder to push the crankshaft rapidly. And that was enough of a crank-shaft speed-burst to generate a spark.