Is the gasoline fresh?
The black plastic one that takes a Phillips is the idle speed adjustment.
The brass one that takes a flathead is the idle mixture adjustment. The mixture adjustment screw is a "Fuel Screw" as opposed to an "Air Screw"
Turning that screw in should reduce the amount of fuel - leaning out the mixture. If you can turn the screw all the way in and you are still way too rich, you might need a smaller pilot jet. If the pilot jet is unmodified, then I'm not sure you can get a smaller one. If somebody drilled it out, then you might be better off with a stock (unmodified) one.
A hotter spark plug might help. Which plug are you using? Try 1 heat range hotter.
Since I don't see an air filter, I assume you have already tried to lean out the mixture by running with no air filter. If not, give that a try and see if it improves.
I'm also assuming that you have the choke off when the engine is running.
How does the engine run at WOT? When you get it running, take the bike for a test run. Give it full WOT for about 10 -15 seconds and then kill the engine while still maintaining WOT. Don't let off before you kill it. Pull the plug and take a picture. Research How to Do a Plug Chop to find more info about tuning this way.
CAUSES OF SPARK PLUG FOULING
If your spark plugs are fouling and keep fouling out, you probably have an engine problem. Normal spark plug deposits are typically light tan or brown in color. Black deposits or heavy ash deposits usually indicates trouble. Some common causes of spark plug fouling include:
Worn or damaged valve guides or valve guide seals. Problems here can allow oil to dribble down the valve stems and enter the combustion chamber. Oil will form heavy black wet oily deposits on the spark plugs.
Worn or damaged piston rings, or worn or damaged engine cylinders. Badly worn piston rings, broken or cracked piston rings, grooves or scoring in the cylinder walls, or even piston rings that have been installed upside down can allow oil to get into the combustion chamber and foul the spark plugs.
Rich fuel mixture. This will produce black fluffy deposits on the spark plugs. If only one or two spark plugs are affected, the underlying cause may be a leaky fuel injector. If all of the spark plugs show heavy dry carbon fouling, the rich fuel mixture may be caused by too much fuel pressure (check for a defective fuel pressure regulator or a plugged fuel return line). A defective oxygen sensor that reads lean all the time can also make the fuel mixture run rich. Check fuel trim readings with a scan tool to see if the engine is running rich (negative fuel trim numbers that are -8 to -10 or more would tell you the engine is running rich). On an older carbureted engine, a rich fuel mixture can be caused by a leaky float, incorrect float setting inside the fuel bowl, a leaky fuel inlet needle valve, or incorrect jetting (too large).
Leaky Head Gasket. This is really bad news because a leaky head gasket can be very expensive to repair. If coolant seeps into the combustion chamber, it will form fouling deposits on the spark plug. A fouled spark plug may be an early sign that a head gasket is starting to leak. The cheap fix here wold be to add a bottle of cooling system sealer or head gasket sealer to the cooling system and hope it seals the leak - at least temporarily.
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