Briggs Stratton back/after-firing - possibly a newbie question but please help anyway

[PaPepper]

I have a brand new power wheelbarrow with a Briggs and Stratton engine. When I start up the cold engine, I usually have full throttle on, and it hasn't backfired several days, but if I have full throttle on when restarting the warm engine, then I got three backfires on start. I tried putting throttle on low when restarting the engine while warm, and it didn't backfire. It seemed to start fine although sometimes needed a bit of throttle to start.

Sorry if this is a newbie question, and I am a newbie to gas-powered engines. Can someone explain why it is backfiring when (A) I start the warm engine with high throttle, but it doesn't seem to backfire if I start either (B) a cold engine with high-throttle or (C) a warm engine with low-throttle.

Thank you to all in advance.

 

[mechanic mark]

Let engine idle at least 30 seconds before shutting down. Try starting engine with throttle at idle position & let it warm up a couple minutes before moving throttle to full.
Read your Engine Manual thoroughly.