We have 2 97 SX 700's. Both are completely stock but one hasa 136" track on it. One has 5800 miles and the 136" has about 3000. On the one with 3000 miles it always fouls plugs. It has been doing this since we bought it with about 1900 miles on it. I can take the plugs out of the 5800 mile one and switch them with the 3000 one, cylinder for cylinder and the 5800 mile one will run fine and the 3000 one will still bog and backfire. Any help or advice would be appreciated? Does it have a faulty cylinder or do I just need to replace the plug wires? Thanks for your help.