Okay, i exaggerated a bit, but it was not a complete lie - at least you're reading this:
Here's the story.
I had not ridden my 1987 K75C for a while as i've been doing a lot of dual sporting. However, i figured i had some time i should change out the oil. I should mention my oil level had been a little low (slightly below dot) for a few weeks, i rode it maybe 40 miles on and off in the state.
I pulled the bike out, start it (started fine) and let it idle with the "choke on" half way. It was idling great, but it hadn't ran for a couple weeks and was stone cold. after about a minute of idling it started sounding a tiny bit different, the untrained ear wouldn't have noticed. i heard a slight clicking sound. I walked over and put my ear closer to the engine to see if i could figure out where it was coming from. I couldn't. I walked away and then it idled high for a second, so i turned around and there was a big pop and puff of smoke from the front throttle body. The vacuum plug on that throttle body was missing. i am not sure if it popped off with the smoke or was gone beforehand and is the cause of the issue. I started it back up after putting some tape over the vacuum nipped, and idle okay. I ended up changing the oil and put it away, Haven't ridden it since, partly because i didn't need to.
What would cause a backfire through the throttle body? Considering it ran okay after the backfire, do you think there is an actual issue?
My next step is to bring it out and check for vacuum leaks.
The only thing i did to the bike a few weeks prior to the incident was change the air filter. i wonder if i messed something up there?
