We quite often get asked to recommend spark plugs to help prevent plug fouling in 2 stroke engines. In many cases a change of spark plug is not necessary, the cause is very often incorrect fuel:oil ratio - especially for premix engines.
It's a common misconception that using more oil will richen the mixture - in actual fact this leans the carburation, the 'thicker' premixed fuel is less capable of evaporation and therefore the fuel:air ratio is increased (i.e. more air and less fuel). So, if you want to run a leaner mix with less chance of fouling due to rich running you need a lower fuel:oil ratio (i.e. more oil).
BUT it's important to differentiate between rich fouling (black carbon) and oil fouling (often wet, sticky), too much oil in the mix will result in plugs being oil fouled instead, excessive oil can even prevent adequate evaporation - the engine won't run at all.
If in doubt always stick to the engine manufacturer's recommendation. Bear in mind that different fuel quality, operating at altitude, ambient air temperature etc can all significantly affect carburation, adjustment may be necessary in order to achieve optimum running.
