Bike wont start!/ fouling plugs?

[feltner58]

My name is Dan I'm new to the forum, I just recently bought a 2001 gz250 with 6k on it, it hadnt been ridden much, I believe the previous owner let it sit for a good while, so like anything I buy that hasnt been run alot, I brought it back to life, ran seafoam through the fuel system, changed the oil and filter as well as the air filter, got the idle set just right and had it running great started right up everytime didnt even need the choke. But last week I rode it to work and when I got home I parked it in the garage. That next morning I went to start it to ride to work again, and it wouldnt start, the starter just kept turning over and over. so I used the choke and it still wouldnt start. I started to look the bike over to see if there was anything out of place, and i noticed that where the choke cable goes into the carb there is a little metal elbow with a rubber gromet that holds the cable in the carb and this whole assembly had come out of the so much that I could see the actual choke cable. so I put it back in as far as it would go and turned the choke off. tried to start it again, no start. so then I took the plug out and looked it it, it was a little black but not overly dirty, I literally wiped it off with my thumb and put it back in and it started right up like nothing was wrong. This would lead me to believe that the bike is fouling plugs or not getting a strong spark. I did accidently run the bike with the choke on when i first got it but it didnt foul the plug and that was over a month ago and it hasnt had any problems until now, it keeps not wanting to start after a undetermined amount of time, the battery is not the original or manufactures recommended size and power (all the lights stay lit and the starter never starts to slow down so no obvious problems with the battery) I dont know if that could be it, I modified the exhaust but I dont think that should effect the starting aspect or the spark plug..............should I get a new plug maybe thats it, a new battery? new coil? Im a technician at goodyear so Im pretty mechanical but bikes arent really to familiar to me... Please help I love riding this bike its my favorite bike Ive ever owned and I would like for it to run for some time to come.