Ok, does it still have the gas in it that was in it when you bought it?
I think that maybe there's too much oil in the gas.
Drain the gas out of the tank and mix up some fresh gas at a 32:1 gas-oil ratio.
If there's too much oil in the gas it can cause the problems you are describing (low power on occasion and smoking like a frieght train).
If the carb is flooding over, you will have to raise the float level slightly, but I wouldn't mess with it unless gas is literally coming out of the overflow tube from the carb.
The absence of a filter would not cause too much gas to come out of the carb into the engine. The fuel flow into the engine is restricted by the needle and seat in the carb. The carb will only take as much fuel into the bowl as the float will allow. once the bowl is full, the needle & seat closes and no more fuel will flow into the bowl. As the engine is running, and gas is getting sucked out of the carb., the float will go down, which will open the needle ever so slightly to let fuel fill the bowl. As the fuel level in the bowl goes down, the float goes down. When the bowl is full, the float will go back up and close the needle.
if too much gas is getting into the engine, it's either a jetting problem or a stuck float.
The only real contributors to fuel getting into the engine is the main jet (you already checked it)
Unless the person who owned it before you drilled out the jet or put in a bigger jet.
If he drilled out the jet or put in a bigger jet, it could be too rich allowing too much gas and not enough air.
Did you look at the main jet and see if there's a number on it or to see if the hole looked like it had been drilled out?
If the jet has a number on it, chances are it's not the original jet. The original jets in these carbs do not have numbers stamped into them, but most aftermarket ones do.
If the jet looks like it has been drilled out, it's quite possible that he drilled it too big.
At that point you will need to get a stock jet and see how it runs with it in there.
If it's too lean or too rich with a stock jet, then you may have to get some aftermarket jets. Or you could solder the hole closed on the stock jet and re-drill it depending on if it needs to be richer or leaner....it can take a lot of time and it's all trial and error.
I think I have a stock nt jet here somewhere, and if you think you might need it, let me know. Maybe we can work something out depending on where you live.
If you need it i'll give it to you for free.