[Badapplesrepair]

2009 Ninja 250r. I’ve done a ton of things to it including rebuilding carbs and valve adjustment. Took a while to get carbs right but eventually the bike got running and was working great. My brother (previous owner) agreed bike was running better than ever. Put maybe 100 miles on it after I got it running in April and tried to run engine at least once a week since then, I stopped paying attention to it in September as things got pretty complicated for me. Today I went to turn it on and ride it. Battery still good everything seemed fine but engine wouldn’t start, after cranking for a while it finally turned on. Engine sounded weak and like it was struggling a bit but nothing else out of the norm until I saw that the muffler was leaking crazy amounts of oil, almost gushing out from where exhaust pipe and muffler meet. Lots of smoke from exhaust coming out too. The oil was black and smelled of gasoline. I got it to warm up and rode it around the neighborhood and even got it up to about 40mph, felt a tiny bit weak but ran pretty well, it died out when I stopped. I can get it to turn on again with allot of cranking and giving it gas but still smokes like crazy and black oil is coming out of muffler. I’m not sure where to start looking here I’m just assuming the worst. Some information for anyone that thinks they can help.
1) last time it ran there was a small leak from the top of generator cover but I figured it wasn’t a big deal and I would handle it later. There is still a small leak and oil coming out looks like new.
2) oil level still looks ok in sight glass.
3) coolant level in reservoir has not changed.
4) looking into the oil sight glass and fill hole there is no evidence of coolant in the oil.
5) looking into radiator and reservoir there is no sign of oil in the coolant.
6) bike temperature was fine while riding.
7) a little bit of stuttering while driving but driveable, I weight 220lbs and the bike was able to handle me just fine.
8) turned it on successfully 3 times, 4th attempt it backfired and I stopped.

I probably won’t be working on it until January but trying to get everything in order now. Any help is appreciated, my plan as of right now is basically dropping the engine and taking things off until I find what’s out of place.