Let it warm up, when the radiator is hot to the touch the motor is warm enough to ride. Suzuki calls for a $34.00 plug to be used, because of reinforced ground strap, which is at a different angle too. The Rm 125 and Yz 125 have more timing from the factory cdi and a regular plug may get too hot, weaken and break. Just keep an eye on it but a br8 or 9, es eg is ok. The letters at the end is the firing tip size. the plug needs to be gapped, 022-026 or no matter what plug you use will foul. Iridiums are nice but expensive. :)