No power and comically large flames out the exhaust

I picked up an 83 750 spectre 4 banger, non running. All stock as far as I know except for a very open exhaust. It wasn't running due to some electrical gremlins that have now been solved, but now I've got some... interesting issues. Bike is a little hard to start and when it does start it shoots up to about 2500 without the choke, eventually it'll bring itself back down to a perfectly decent idle, I already replaced the block to carb rubber boots. While it's running it is absolutely pluming smoke out of the headers and "muffler" and after warming up will shoot 4 foot flames after a rev and on some occasions will have a flame just sitting in the end of the exhaust while it's idling. Now as cool as that is, that's not normal. It's fuel fouling spark plugs pretty hard, bogs down when under load and doesn't seem to want to rev past 4k when in gear. Obviously it's running rich. What can I do to fix this? I'm going to try and back the mixture screw out to lean the mixture and see if that helps. I have no clue what the previous owner was doing with this so it's possible there's a horrible jet kit in these carbs, but I find that unlikely. 

Also one of the carbs is leaking out of the inlet when the bike is off. Not really sure what that's about either. Link is to what my bike is doing right now.  youtube.com/shorts/SWVqw57oAIk?feature=share

You're probably getting gas into your engine oil.  I wouldn't run it like that!

I'm not running it at all right now. I need to figure out why it's acting like this though.

Could be a stuck float valve, a float that does not float, or a jet that has fallen out. Have you checked the fuel level in each carburetor using the clear tube method?
it is also likely that the petcock (fuel valve) has failed and needs to be rebuilt.

Is the engine oil level unusually high? If you remove the filler cap and give a sniff to the crankcase, does it smell like gasoline in there?

So I should probably just rebuild my carbs to be safe then? Or would a deep cleaning suffice? 

And would the petcock cause the leaking issue or the running stupid rich issue?

Personally, I would want to diagnose the problem before diving in. If the bike has been sitting unridden for more than a month or so, cleaning the carbs will likely be needed along with rebuilding the petcock. The petcock is supposed to stop the flow of fuel out of the tank when the engine is not running. Ideally, if that happened, the float valves should prevent overfilling of the carbs, as long as they are not dirty, partially clogged with dried fuel, or badly worn.
The brass parts in the carburetors rarely need replacing. Most of the time a thorough cleaning and new gaskets and orings will do the trick.

If there is fuel in the oil, an oil and filter change are needed before trying to start it again.

Okay, I'll take the carbs back off and clean em up. I'm still not sure I understand what could be causing them to run stupid rich and dump that much fuel into the exhaust unless they were jetted poorly. Would a dirty carb be able to flow that much fuel?

Just my experience, but it's not from a KZ or the bike.

I once had 86 Toyota Corolla with 4-AG engine (yeah, twin cam one). Modified the engine to have 2 twin 40mm Mikuni's on it. Long story short, I can't remember what we were doing at the time, I had the exhaust off, just the headers on it. I think we were just making sure it start. Yeah yeah, I know. But hey, I was young and stupid. Anyway, flame shot out at the end of headers. Never saw that before. Found out my main was waaaaaaay too big, and as soon as you closed the butterfly, that unburnt fuel came in contact with air outside, just enough fuel to ignite, and created the flame (according to my mechanic friend). Exhaust was still hot enough to ignite it. According to him, when you have the butterfly open, probably was too much fuel to ignite it. Still remember this because I thought it was cool, but I knew it was not right and engine was running rough.

I also saw flame that came out of carb from V-8 engine ( I drove and modified various V8 car in the past) , but that's usually is a timing issue.

Not too sure any of the experience helps, but thought I'll post it here.
 

A stuck float needle can cause a lot of fuel to enter the cylinder.

If one or more of the float valves is not closing, fuel will flow into the carb body, then into the cylinders. From there it can run into the exhaust, and past the rings into the crankcase, depending on where the pistons are and which valves are open. 

that's actually pretty helpful info for my case. I wonder if the guy before attempted to jet these and just absolutely botched it.