wocketman,
Here's how Albert explained it to me.
When the gas valve pulses at the beginning of the start sequence, it is purging all of the air from the gas line to the combustor, and replacing it with Powermax gas.
The valve opens fully at 1800 rpm during spooldown, the ignition is turned on for one second, and the fire lights. The starter motor re-engages, the fuel ramp-up starts, and away we go.
The start sequence wouldn't be as smooth without the air purge cycle.


Harley Condra
BVM REP