A 10 year old K&B 40 NEEDS to run rich, "lots of fuel coming out exhaust and it was dark". Running it lean can ruin it.

You want it "blubbering" rich (called 4 cycling) at full throttle for the first full tank at least. Then, you can lean it out a little, just until it starts to break into a 2 cycle run. (Preferably back and forth between 2 and 4.) Run it this way for another tank or two.

For the next couple of tanks you can run it on the rich side of lean. (All of this at full throttle.)

Once you have at least 3 to 4 tanks through, 4 to 5 is better, you CAN start running it leaner. "I am still getting some excess fuel coming out...it is minor though and it is clear." May be too lean.

If the engine is bench mounted, the easiest way to determine if it's too lean is to "pinch" the line feeding the carb. If the engine just quits, it's too lean. If it picks up some RPM before it quits, it's probably about right.

You don't EVER want to run your engine at peak RPM because once in the air they unload a bit and lean out further. Can do a lot of damage quickly. Tune it to peak, then back off 400 - 500 RPM. If you do, the engine will last for years. (If you don't plant it first. )
Dennis-