Backfiring, flames coming out of exhaust and cutting out

check voltage to ign at least 11.8v
check for water in fuel

could b faulty coil

Check your fuel cutoff solenoid, if your motorcycle has one. The role of the cutoff solenoid is to prevent fuel from entering the cylinders and igniting (backfiring) after you've shut it off.

I also have a 1400 intruder, it backfires, and cuts off often at idle. I have tried many things.. HELP

It could be the speed of one carburetor is faster than the other. This causes the backfiring as well as forces one cylinder to run lean which causes the tapping noise. You will experience an identical tapping or "ping" when you get close to empty on main fuel and need to switch to reserve. Most likely you or the previous owner unknowingly adjusted the speed of the rear carburetor down because of the high stock idle not realizing the front carburetor needs to be slowed down to match. While running simply turn the idle adjust screw clockwise on the rear carburetor until the idle smooths out and the backfiring/tapping stops.

If they cant duplicate it your good.Usualy with backfiring i would make sure to eliminate any exhaust leaks. The dealer is inexperienced at solving compound problems,(sorry) not picking a fight, but sometimes cleaning is not goog enough,I went through this with a 1400 Intruder.several attempts were needed to get the two carbs level on the same line with each other.so the floats would work properly together,then set fuel flow and the air flow through the ventouri in the carbs.Also i had to make these adjustments while level (not on side stand) The floats were very sencitve to needle valve to seat adjustment(bent to open or close some of the flow)

Did you sync the two carbs? If not the rear may be getting all the gas from the rear carb and none to the front. Twist throttle engine off and see if front carb cable is pulling the carb open.
Also unscrew the spark plug boot from the front spark plug wire and trim 1/8th inch off the wire and screw the boot back in. The plug wire end may be corroded on that wire.

sounds if you have a burnt valve/s somewhere

Hi ...... If problem continues try switching petrol off at the tap overnight or when you stop the bike. Sounds like petrol is leaking pass the petrol tap and sitting in the bores and exhausts, soon as you start it up it's igniting in the pipes. Remove the plugs and the colour will indicate how the jetting is set up.