Re: 929rr motor swap won't run backfires
have you made sure all the spark plugs wires are correct order? If the middle two are swapped over, which is very easy to do, it will start but may cause the back-fire you're having. Worth a look anyway.
reading codes is straight forward. Ignition and kill switch off. Short the Check connector RH side by the battery (two pin connector - make sure you've the right thing but the should only be one there!). turn the ignition on and kill switch on, do not start. The bike will power up and the MIL will flash if there are codes stored. if it stays steady red then no codes. if it flashes 6 times that code 6, 1 flash followed by a short gap and say 2 flashes is a code 12. If there is more than one fault logged there will be a long gap between the first code and the next. when it gets to the last code it will start again from the first one again. There is a table of the code in the internet, workshop manual etc. There is also a guide on how to clear the codes but I cannot remember off the top of my head.
Hope this helps.