Had and interesting problem this weekend. First weekend withthe new boat. Twin 502 built to about 560 hp. Port motor ran fine, starboard motor dropped from 5000 rpm down to 4000 rpm. Starboard motor motor ran about 60 degrees hotter oil temp and minimal difference water temp. Starboard motor under load kept stalling. It seemed that this problem must be something simple. I started by pulling plugs and found the three plugs on the starboard motor not tight at all and found that the electrode was burned off. Could the fact that plugs were loose be the cause of the burned electrode higher temps and the lack of power or could the plug being loose be a result of something else?

I've changed all plugs in both motors now. Do I have anything to worry missing electrodes maybe floating around in the cylinders?

Any suggestions? Thanks.

Runningf lean in those cylinders.That would cause the higher temps and the burnt plugs.Thelean condition may have been caused by the loose plugs but i would check into the injectors and fuel pressure.

If the plugs were loose this would cause you to go lean, and burn up the plugs. Were the ones that were burnt up , the ones that were loose?

other then not being tightned properly is there a reason they could be loose? Temp expansion and contarction?

I have not seen where a plug looses up. May happen, just have not seen it. I have never had a burnt off tip and not had other engine damage. Hope you are lucker then me. Might do a quick compression test.

I second Jack!! Leaned out and/or too much timing! Not a good sign.

Or spark plugs = too hot =wrong heat range!

Loose spark plugs pull air into the combustion chamber and lean that cylinder. Replace the plugs and try again.

Plugs will not loosen if tightened properly. Those particular plugs were not tightened from the get go.

My brother had a loose plug in his crusader 502 and blew the spark plug electrode out of the middle of the insulator due to the heat from detonation. You could hear the whistling from no electrode in the plug after it popped the electrode out of the plug. The wire was laying in the bilge with the electrode attached to it and the insulator was still screwed into the head. Motor also ran like crap with just one plug loose not to mention three. Just like you saw. Slow drop off in rpm.

The loose plug can definitely burn the electrode off.

No need for any other action other than to replace the plugs if they were truly loose.

Oh, BTW if you have a hard time with a spark plug socket hitting the exhaust or whatever try a regular long 5/8" socket.

Make sure you have the correct style plug for your head. There are two diff. types one has a metal gasket for alum. heads and the other has a flare for iron heads. I have seen the gasket type on an iron head back out! Just an idea.