#2 spark plug keeps fouling.(Soot on plug not oil)

1993 mazda b2200 truck 4 cylinder with carb. 5 speed manuel. About 150000 miles. #2 spark plug keeps fouling with soot not oil. Compression test was #1 120 psi, #2 120 psi, #3 90 psi, #4 100 psi. Does not appear to be flooding other cylinders are not fouling. Engine probaly needs a rebuild, but I would like to find out what is causing this before I do. Check engine light has been on since I had this truck, 2years. Thanks