I'd try what I call "fuse-staging"; have a piece of waterproof cannon fuse in the nozzle of the upper motor with the end touching the top of the booster motor grain. The fuse is consumed very quickly, and assures good ignition of the upper motor as it is in the nozzle touching the grain.
I have done this several times and it has worked great.

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !