Motorcycle Classics tech expert Keith Fellenstein solves a fouled spark plug problem in a 1973 Norton 850 Commando. The very last Norton Commando built, a 1977. I never get fouled plugs using N3C Champions.I burn very little oil in the engine so they stay clean. Norton Commando, OSSA MAR. (70 and 73) and they do fine. I read a long entailed article on spark plugs and it basically said that a modern spark plug cannot be cleaned and still be good. It can be usable but it will be greatly compromised.
A spark plugs gap directly affects the tip temperature and the voltage necessary to fire the plug. NGK spark plugs traditionally leave the factory pre-gapped for their most popular application. However, a plug may fit hundreds of engines, from cars to golf carts.
Gapping the plugs to your engine’s specifications is important to prevent pre-ignition, detonation, fouling and poor fuel economy. Even if the preset gap matches that required by your engine, it is always good practice to physically check the gap as it may have shifted during transportation (not all spark plugs are packaged in a way that protects the firing end ). Gapping is not recommended on multi-ground plugs. Fine Wire Plugs Plug manufacturers typically warn against gapping fine wire spark plugs due to the fragile nature of their electrodes. They say a fine wire plug will outperform a standard spark plug, even if not properly gapped. However, NGK understands a spark plug can only operate to its optimum potential if properly gapped.
Proper gapping technique should be followed with any spark plug, but special care should be taken with fine wire plugs. NGK will not warranty a plug who’s center electrode is snapped during gapping. Modified Vehicles Proper gapping is especially essential in modified vehicles.
The ignition process is affected by increased compression, fuel type, nitrous and high output ignition systems. A plug’s gap must be adjusted to account for these changes in engine conditions and ensure a successful ignition sequence. Opening the gap presents a larger spark to the air/fuel mixture, maximizing burn efficiency.
However, after raising compression and installing a turbo, a smaller gap is required to ensure ignitability in the denser air/fuel mixture.
The codes used by the various manufacturers give some information about the plug types. The first digit represents the thread size, followed by a number which reflects the heat range of the plug.
The Champion and NGK plugs match well in this respect, but do not necessarily match well with others. This is because some have wider heat ranges and one plug may cover two from another manufacturer. As a rule of thumb, for NGK and Denso, a higher number means a colder plug whereas for Champion, a higher number means a hotter plug. The next letter describes the reach of the plug, except in the case of Champion where the first letter describes not only the thread but also the reach. Any other letters cover special features or materials used or if the plug is for competition use. A 'P' in the NGK range, a 'Y' in the Champion, or a 'D' in the Bosch range means that the plug is a projected electrode type.