Why my spark plug keeps on fouling?

alright guys lets see if u can help me out again. I got a 96 kx250 2 stroke dirt bike and every time i start the damn thing it fouls a plug. Even though i blow it out each time i start it and right before i turn the engine off.me and my family have been riding these things since the 70's and haven't had ne trouble like this. it probly went through about 6 spark plugs in one day. Also after it is running and i get to ride it it doesn't seem like its running right. it has a dry rotted carb but we put some pb blaster on it and started it and it didn't seem like it sucked ne in so i don't think its getting to much air. idk what to do for it, please help me