High-quality standard spark plugs from NGK with nickel alloy electrode.
What is important in engine tuning is the correct heat range of the spark plug as otherwise the cylinder will overheat or the spark plug will foul.
A cold spark plug will transfer more heat to the cylinder head and the electrode will be prone to fouling, as the cleaning temperature cannot be reached.
A hot spark plug transfers less heat to the cylinder head; this is where you should be careful as the cylinder can overheat and there is a danger of piston seizures.
Many rev counters require a resistor spark plug in order to function correctly; conventional spark plugs can lead to extreme jumps or absurd readings. So if you have a rev counter, you’d better go for the slightly more expensive resistor plugs to be on the safe side.
Short reach = 12.7mm thread length
Long reach = 19.0mm thread length
NGK short reach CR7HSA (WR4CC), resistor type