Usually a combination of slow cranking and too much timing. Easily cured with an MSD box that automatically pulls the timing back on start up, or a toggle switch to shut off power to the ignition. With the ignition power switch off, crank the engine over with the start switch, when it's spinning good, turn on the ignition.... Old timey fix from back in the days of high compression engines and trying to get them to crank when they're still warm and it's time to get up to the line for the next round........