I changed my mainjet from 168 to 175 and lowered te needle from clip 4 to #3 (WR400 '99, WRtiming, YZ exhaust). The bike rides pretty good, but the spark plug is black. When i start the it when it's cold i have to be very carefull, I miss the start, I have to clean the sparkplug or it won't strat anymore. They always say the sparkplug must be almost white....do i have to worry about its colour if it rides good ???