OMC V4 115 Runs without spark plugs!!!!!!!!

[mcbutler]

Hi All,<br />I have an OMC 115 V4 turbojet in a rage 15 Boston Whaler.<br />Yesterday while running the engine on the flushing attatchment I revved it and when I returned the throttle to idle the engine stayed at full revs. <br />I turned it off at the key...nothing happened.<br />I pulled off the lanyard.....nothing happened.<br />I pressed the emergency stop.nothing happened.<br />In desperation I grabbed the plug leads and pulled ALL FOUR off....nothing happened.<br />Now as you can guess I am panicking a little as my engine seems to be commiting suicide.<br />I grabbed the fuel pipe and bent it double, after 30 seconds or so the engine slowed and stopped (thank God).<br /><br />Has anyone any ideas for a cause?<br /><br />Remember the plug leads were OFF all four of them.<br /><br />Many thanks,<br /><br />Mark...

 

[captkid]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

Has anyone any ideas for a cause?

haunted?

 

[orion208]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

Better call "Unsolved mysteries".

 

[cobra 3.0]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

possessed!!!!

 

[JB]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

Very common, Mark.<br /><br />It is called thermal runaway. The engine goes into a Diesel cycle and revs uncontrollably.<br /><br />The only way to shut it down is to cut off the fuel.<br /><br />2 stroke engines should NEVER be revved over about 1200rpm with no load.<br /><br />Thank your luck you don't have a rod poking through the case.

 

[rodbolt]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

and now ya know why ya cant be a throttle jockey on the trailer. I hope all that is wrong is some slightly puckered skivies.<br /> good luck but dont try it again. a runaway is funny till it happens to you<br /> PS yes I have had my share

 

[P.V.]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

Actually, the right way is to not wait for it to run out of fuel (could take longer than you care to wait or even be near that beast) but to add attional fuel via the choke (primer) and flood that sucker out!!

 

[Destin]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

I'm not an outboard expert, but I can't understand how that could happen if the throttle plates are closed. I guess there is no positive throttle return linkage on an outboard. I would install extra throttle return springs.

 

[JB]

Re: OMC V4 115 Runs without spark plugs!!!!!!!!

I agree that it doesn't make sense, Destin.<br /><br />A runaway engine doesn't care where the butterflies are. There is no load, so it doesn't need to make any more power than is required to spin the crank. With the diesel combustion taking place earlier than spark ignition it is behaving as though ignition was far advanced.<br /><br />I don't think additional throttle return springs would help.