How do i improve in math

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If by black you mean sooty then it is running too rich.
Check your air filter, although all plugs would be sooty if it was blocked or restricted.
Try a new plug or swap plugs over to eliminate a dodgy plug. Check coil resistance (primary and secondary) to see if it is not breaking down.
If you can get to the air/fuel adjustment screws do the following:
1. On the properly running plug carefully screw in the adjustment screw until lightly seated. Do not over tighten, just til it seats. As you are doing this count the number of turns you have done. I count a quarter turn as 1, so if it goes in one and a half full turns I will have counted to 6. I find this more accurate than the number of full turns. Now unscrew it the same number of quarter turns and it will be back where you first started.
2. On the screw that adjusts the faulty plug, again count the number of quarter turns to a light seating. Usually it should be the same as the other but not always, although it shouldn't be that far away. Back it off to the same number of quarter turns as the first one was set.
Now try running the bike and see if there is any improvement. If it is worse adjust it back to its original setting.

could be bad fuel. could have water or condensation in the tank. also if you let the level drop low it could start sucking sediment that settles in the bottom of fuel tanks

Possible fuel filter, fuel pump issue. Check out these items and let me know what you find.
I hope this info helps!~subyguru~

Sounds like ignition components may need replaced like the coils and wires.

Ignition key on, throttle three quarters on, full choke, press primer 3 or 4 times, pull cord. Should cough, maybe start and run rough, then as it's chugging, turn choke to half, then quarter choke, let it warm up slightly, then choke off.

Fresh fuel? Does carburetor have adjustable jets? Turn the high speed jet (at bottom of float bowl) about 1/4 to1/2 CCW (looking at bottom of bowl). If no improvement, carburetor should be torn apart and cleaned. This also applies if there are no adjustable jets. Is there a fuel filter anywhere?

check ur timing firing patern could be off