Yesterday while sitting at a stop light my bike started running rough and backfiring. I had just ridden 15 miles from work without issue on the highway. Needless to say, I stalled it at the light. Got it going and feathered the clutch. It ran rough but once it got to about 4,000 rpms there was a huge surge in power and it was smooth again. Another, stop light, and I could tell the back firing was at about 3 times per second. Very cyclical.
When I got home I shut it off. Started it up a few minutes later with the kickstand down and it still ran rough and back firing at about 3/sec. It would backfire faster as I gave it some throttle. From the exhaust there is a distinct burnt metallic smell.
Some side notes.
Filled up 2 weeks ago.
Washed the bike 2 weeks ago but hadn't ridden since then. I did run it to shake out any excess water.
The side stand has gotten easier to get down lately, which is why I tested it with stand down in neutral.
We do have roof rats in the neighborhood and the dogs were particularly interested in sniffing deep into the bike. However I looked and I don't see any signs (prints, olives, etc.).
8,000 miles, last service at 6,000 miles.
Battery cable looks to be securely connected.
Where do I start diagnosing this? The sudden onset makes me think fuel (if it were carberated), but it would seem more like no spark and the symptoms are no spark and gas igniting in the exhaust. But then it clears up at higher RPMs.
Also it's all stock.
