It would take some engineering to get the ignition timing off. It comes right off the crank just like your 1500.
When I reread my post I can see that I wasn't clear at all about what I was trying to say. I know that some bikes were carbed and some had electronic fuel injection. When I said the ignition timing I wasn't only talking about the spark I was talking about the timing between the spark pulse and the injector pulse. I don't know if they both get their signal from the same source or not. That is why I can't be specific on the cause. My point was the conditions that could cause this backfire or misfire. Pre-ignition would cause it to backfire through the intake on the compression stroke and late ignition could cause it to backfire on the exhaust stroke. A very slow combustion could cause this too as in the case of the fuel still burning at the start of the exhaust stroke. As I said, I don't know very much about his engine so I was speaking in very general terms on things that could cause backfiring.