95% of the time its your glow ignitor not being hot enough. Charge it up to its max , replace the batteries if its that type. If that doesnt do it , give your glow-ignitor a nice clean in some alcohol to remove the oils and such. Dry it and retry.

I know with the ones that use D and C cell alkalines. You get maybe 1 minutes worth of power time thats effective enough to start the motor its first start. Otherwise you gotta give them a rest so they can return there power back to a high enough level to start your car.

I highly suggest the hobbico lattern style battery starter or a starter box power panel if you have one. This will give you ample time and juice to start these big boys.