+4 has proven to be a typically safe option. There are two areas to read the spark plug when checking if the motor is happy with current timing. Most will look at the strap near the 90* bend. A nice line seperating two colors indicates happy. Also look how far the soot is from the top of the center electrode. You want it nice and tight. If it's running clean up in to the plug beyond a millimeter (by eye, there are other precise ways to measure) a change is needed. Sent from my iPhone using Tapatalk