What's with Runaway?

[UpstNYer]

Have seen posts here that if a 2-stroke engine is revved too high under no-load conditions that RPM may runaway and reach such high values that the engine self destructs. Can't this phenomena be halted by retarding the throttle or quickly shutting off the ignition? Or does it happen to quickly for that?<br /><br />Is there some magic RPM above which no-load revving might lead to runaway; but below which it's not a concern?<br /><br />Got thinking about this yesterday when my 90HP Merc Classic reached 3000RPM on a flooded start before I yanked back the throttle.

 

[Terry H]

Re: What's with Runaway?

I only had one runaway motor and it was a omc v4 on muffs. I don't think I intentionally revved it much pas 2000rpm when it took off. Fortunately I was at the controls and shut it down quickly...no damage done, but my buddy back at the motor was in duck mode...just a thought<br />

 

[JB]

Re: What's with Runaway?

If an engine goes into thermal runaway turning off the ignition will not help. The engine is in a Diesel cycle.<br /><br />You must shut off the fuel.

 

[Terry H]

Re: What's with Runaway?

JB...I guess mine weren't in thermal renaway cause it wasn't warmed yet, and it did shut down when I turned the power off...and my buddy the omc tech hit the dirt.

 

[Mettaree]

Re: What's with Runaway?

Unloaded high RPM extermely rough on rod bearings. Things tend not to stay glued together when that happens.<br />