kx 250 oiling plug up not black oil

[xx1kx250]

kx 250 oiling plug

hi all have a kx 250 1997 and it had engine rebuild 2 years ago but was never run.
i recently run the bike in have only been out a couple times now its killing plug
first time after 2 hours
then after 1 hour
now its 2min running
exhaust is black smokes a bit
could rear silencer be clogged
or crank seals maybe
or ignition prob
the plug is oily but not black
has fmf fatty exhaust and carbon reeds jetting is ok for the pipe not sure bout reeds
bike was running really strong until this
any help would be appreciated
the oil is black just rechecked
would a hotter plug be worth trying

 

[SBC383STROKER]

Check the condition of the right main seal. Check your jetting, it might me on the rich side.