What causes backfiring??

[Roverland]

When firing up the V6 landy in the mornings it back fires quite loudly when i rev it. Whats causing it????

[Rich_P]

Overfueling, or poor mixture causing poor detonation of the fuel and allowing some fuel to enter the exhaust.

[Timi]

Overfueling, or poor mixture causing poor detonation of the fuel and allowing some fuel to enter the exhaust.

Onions!!!  Or christmas sprouts!

Possible break down of HT lead miss fire would be evident, ignition timing choke malfunctioning possibly.

Any good what was the answer?

[mark.yellow.series.3]

is youre timing to far advanced? that will cause it.
KandN's with a sports exauste also gives you a bit of popping 8)

[James.Harwood]

is the "back Firing" when increasing in revs or after on the overun (revs decreasing)

On overun this is normal with a sports exhast or broken exhast and a cylinder head in good condition.

When increasing the revs it could be anything listed above plus more.  

One thing to look for is 'blow back' particularly if you use unleaded fuel without a unleaded head.  Take the air pipe off the top of the carb and rev engine, if you have blow back you will notice the charge being 'blown back' out the carb (can be unburned or burning when this happens).  If this is the case you may have burned out valve seals or defective valve springs.