What would generally be the reason for a backfire, let say it is idling and then you rev it in neutral to 3k rpm and let off, a backfire occurs

would that be too lean or too rich?

 

Too rich is the only way a "backfire" is caused by extra fuel burning in the exhaust.

In reality, it is not a backfire. A true backfire is when the combustion is too soon and some exhaust gases go backwards out the intake.
Thus a backwards explosion or backfire.

But we Americans love to f**kup terminology and language.

A more correct term would be "exhaust farts"!

 

lol, you are right, thanks for the info.

 

ROFL