Johnson 88 HP power loss & melted plug

[Puttdrainer]

I bought a 16' fiberglass speedboat with a Johnson 88 HP outboard last fall. I have taken it out on several lakes this year & probably have 6 or 7 hours of actual drive time on it. <br /><br />A few weeks ago my daughter hit some rocks at very low speed....and the boat seemed to lose power at that time. The edges of the prop were pretty torn up and I installed a new alum. Mich prop 13 inch with a 19 pitch (011004). The original had a 21 pitch. I was hoping this would bring some of the RPMs back. The boat cornered better but the power loss continued. It also continued to stall at idle speeds when docking.<br /><br />Tonight I checked the plugs and 3 of the 4 seemed normal. However, the upper right (starboard) plug was VERY clean....but additionally.... the metal arm (electrode / flange?) had a piece missing on the "outside". The inside surface of the arm/flange that sparks across the gap was OK. <br /><br />The plug almost looked like something came flying out of the combustion chamber and slammed into the spark plug "metal spark electrode arm". There were a couple little pieces of metal that are stuck between the center of the plug and the outside insulator. <br /><br />I assume that when I start it back up the engine will probably be hitting on all cylinders and the RPMs will probably go back to normal. Still have to test but I expect so. However, I am worried about "why" the little arm of the plug either melted or something slammed into it and chipped part of it off. <br /><br />The gap on the other 3 plugs appeared to be 0.030. I understand that the engine originally was supposed to be set at 0.040 but in later years the 0.030 setting was recommended. The plugs in the motor were L77JC4 plugs which match the recommeded plugs per the shop manual. The boat is a 1990 but the engine might be earlier. Serial is 08275107.<br /><br />I've read that water can sometimes cause the plugs to be clean....but am thinking that nonfiring / noncombusted fuel might also tend to clean away deposits. <br /><br />Any information would be appreciated.<br />Thanks!<br />Puttdrainer

 

[Bass Runner]

Re: Johnson 88 HP power loss & melted plug

Hold everything i think you better pull the head sounds like you got some scoreing going on in there, its not that expensive for a head gasket and might save your motor, are you sure the fuel mix is right and not overheating?

 

[Puttdrainer]

Re: Johnson 88 HP power loss & melted plug

I don't understand why you think it would be a head gasket but I will keep that in mind. Any info you could give me on "why" would be appreciated.<br /><br />Fuel mix should be fine. I have been using premium (93) octane fuel plus TCW3 oil at a 50 to 1 ratio. Is 93 too much octane ? There was some old fuel in the tank from last year but I think it has been burned long ago by now.<br /><br />I am also wondering if setting the plugs at a 0.030 gap rather than at the original 0.040 gap might cuase them to run hotter....I have no sense of how the change in gap affects "hottness" of the plug but assumed that it would change it one way or the other.<br /><br />Thanks very much for your interest & help .... it is truly appreciated.

 

[Walker]

Re: Johnson 88 HP power loss & melted plug

He doesn't think its a bad head gasket. He means that you should pull the head to check for piston and cylinder wall damage and you will need a new head gasket for reassembly.

 

[self taut]

Re: Johnson 88 HP power loss & melted plug

changing the gap size dosent really change the "heat" of the plug.that is done by the length of the plug itself.i believe a shorter plug runs hotter longer runs cooler.someone correct me on that if im wrong.changing the gap changes the the amount of space the spark must cover in order to connect with the other side basicly it determines how long the spark actually exists. the shorter the gap the shorter the spark life.( not plug life)the wider gap gives the fuel more time to ignite.determined by the manufacturer, by what fuel is recomende and type and amount of oil mixed.i would likely leave the gap set as recomended, and would ask a mechanic about changing gap before doing so.i sorta get the feeling that the small piece of metal wedged between the electrode and the insulator created a bridge for the spark.almost grounding the plug before it had a chance to get a proper spark.this would help explain the partial melting of the plug.I wouldnt pass up on the possibility that you may have some cyl wall damage though.anytime you find loose metal in a cyl you need to check it out imediatly.better to find out now and spent that small amout of money replacing a head gasket rather than wait a season and replace a sleeve and a piston and whatever alse thay may get damaged.

 

[self taut]

Re: Johnson 88 HP power loss & melted plug

just re-read the post.i missed something there.

The plug almost looked like something came flying out of the combustion chamber and slammed into the spark plug "metal spark electrode arm".

new thought Yank that head.strongly agree with bass runner here.sounds like a good possibility you have broken metal floating inside the cyl.maybe a piece of a ring or whatever.strongly suggest you pull that head and look before you runnthe motor again

 

[mattairconman9]

Re: Johnson 88 HP power loss & melted plug

I just went thru the same ordeal. I was cruising along and the motor went down to 1/2 speed, then I got an awful knocking noise and crushed plug. I pulled the motor apart and found the connecting rod thru a bearing and smashed up the whole piston. Well $1000.00 dollars later I'm still working on the rebuild myself without determining what caused the problem to begin with. Good luck.

 

[voodoo]

Re: Johnson 88 HP power loss & melted plug

matty...<br />rod bearing failure is most often caused by poor lubrication.

 

[Puttdrainer]

Re: Johnson 88 HP power loss & melted plug

Thanks everyone for sharing your experience and taking the time to give me good advice. <br /><br />After work today I took the spark plug to a local shop & the mechanics assessment was the same as yours.....I need to pull the head & see if there is anything floating around in there.