over tightening Spark Plugs, especially when installing them in a hot
engine with aluminum heads. A plug that is over torqued when the engine
is hot can cause crack(s) in the head as the engine cools down.
Generally speaking, you want to run as wide a plug gap as possible.
Having to reduce the size of the plug gap once it has been well
established can possibly been an indication of problem manifesting in
the ignition system. This is common in the magneto systems as they
generally need smaller and smaller plug gaps as the magneto
plug that appears to have a pinkish hue to the electrode has either been
overheated or has been subjected to pre-ignition. Pre-ignition is the
result of the cylinder firing before the plug fires. Carbon buildup,
untrimmed gaskets, sharp edges, too hot of a plug are just some of the
black splotches on the insulator of the plug can be caused by
detonation, which is basically an explosion in the cylinder after the
plug has fired. Shitty fuel, too far advanced timing, engines that have
seen a lot of miles, or were improperly assembled can suffer detonation
when oil gets into the combustion chamber and reduces the octane of the
fuel. If that happens, a rebuild is the only repair, otherwise retarding
the timing, and/or using better fuel usually does the trick.
deposits on the plugs means that the piston is overheating. This is
caused by either a lean mixture, or having the timing too far advanced,
or a combo of both.
have the head off, check the projection of the plug into the combustion
chamber. If there are threads showing you will want to either use
washers to pull the plug back up or better yet switch to a shorter plug,