527; It sounds like timing could be the cause of your preignition or detonation problem! As far as the difficult starting (this is based on an experience of mine) take a close look at the wires from your coil back to source. Your ignition is powered two ways, during the start cycle a full 12 volts are supplied to the coil from the starter relay. When the key is returned to the ignition position power is run through a resistor (usually on the firewall). if the wire from the starter relay to the coil is broken or poorly connected you end up with just the reduced voltage during start and could cause difficult starting.