You should pull the plugs first, could just be a fouled plug. Gap is .030.
Coil install is fairly easy. Remove the shroud, rotate flywheel so magnet is away from coil and remove coil. When mounting the new one, pull the coil away from the flywhl. and just snug the bolts. Then rotate the flywhl so the magnet is under the coil and insert a business card between em. Loosen the bolts holding the coil and the magnet will pull the coil in , setting the gap. Tighten the bolts and rotate the flywhl while pulling the card out. The correct gap is .008 - .016.
A card is around .010, so that works out pretty good. Anything non-metallic can be used as long as it's in the range.
Ya wanna clean the heads/fins while ya got the shroud off.