What happened to this spark plug?

[Andyfender]

On the water today my engine would not give me full throttle. When I got home I pulled the plugs on my 1978 Johnson 35 HP.
Installed were Champion UL77V. We some help with the folks on Iboat I was told the spark plugs I need are either QL77JC4 or L77JCF. The UL77V does not have the ground electrode. Does it matter I don?t know. That being said is there a logical reason why the plug (UL77V) ceramic insulator cracked?

Thanks,

Andy

 

[ezeke]

Re: What happened to this spark plug?

Either someone dropped the plug and cracked the insulator or it was cracked by the socket when loosening or tightening. Except for the dirt, the electrode gap is exactly as it should be for a surface gap (V) spark plug.

I've attached a picture of four new UL77V surface gap plugs.

 

[1946Zephyr]

Re: What happened to this spark plug?

From what I understand, that engine calls for QL77JC4 gapped at .030. That's what I've read on other postings. I have seen those plugs used in bigger motors and Mercs, however.

If the ceramic was broke on both plugs, then my bet is that someone used a bad plug socket on it.

 

[ezeke]

Re: What happened to this spark plug?

From what I understand, that engine calls for QL77JC4 gapped at .030. That's what I've read on other postings. I have seen those plugs used in bigger motors and Mercs, however.

If the ceramic was broke on both plugs, then my bet is that someone used a bad plug socket on it.

See, that's part of the problem. When the motor was manufactured it called for a surface gap plug - a L78V - it still shows on the parts diagram on BRP's current listing.

Then, in June of 1988, OMC issued a service bulletin (#2197) recommending the use of the premium QL16V surface gap plugs as an alternative to the L78V and others for certain conditions. So the service departments used them. The QL16V runs a little hotter than the other plugs so it stayed cleaner when trolling and idling.

Since then the plug recommendation for general use for this engine has changed to the QL77JC4 and appears in the updated lists of most dealerships.

This forum member has already had this subject up, so much of this is just repeating. http://forums.iboats.com/showthread.php?t=410853