spark plug

[Max_Door]

One of the spark plugs on my 56 johnson 15 is bad. The insulator does not appear to be damaged, the plug does not look worn out, but I have no idea how old the plugs are. I know that it is bad because I can swap cylinders and isolate that it is the problem. The plugs are c j6. I cleaned the carbon off the gap areas and now it only will almost fire, still no good. <br /><br />My question is, can a plug look good but still be bad? I have always been able to clean and correct a fouled plug before. Just wondering. Also, why such a heavy tarnish of carbon? I guess that is a symptom of something wrong?

 

[jamesboater]

Re: spark plug

hello going from experiance i have brought new plugs that are bad and wont fire, i have flooded engins and then found the plugs wont fire even after cleaning, if i was you i would simply replace the plugs, you mite not be able to get that plug but im sure there is an equivalant to it,

 

[Paul Moir]

Re: spark plug

Champion J6C gapped at .030" is the correct plug for your engine. I don't think there's much difference between it and the C J6 other than it's a full sized plug. Might as well get the right ones though.<br />Run the new plugs at full throttle on a boat for a couple minutes, then cut the engine, pull the plugs, and examine them for appearance & differences. If they're still building up carbon then you're probably running rich.