Xjr throttle valve

The spark plug is wet, indicating that the cylinder is not burning well. You should check the reasons for the bad. Unplug this cylinder line first, and when the other three cylinders are working, let this line be grounded to see if the fire is normal. If the fire is normal, remove this spark plug and insert it in the high-pressure cap to see if the fire is normal. If it is abnormal, replace the spark plug. If it is normal, plug the spark plug hole with your finger and try to see if the cylinder pressure is normal. If all these are normal, then check whether the carburetor of this cylinder is too thick. The factory setting is, screw it to the bottom, and then turn it to 2 1/2 1 turn. I hope I can help you.