If a groove is found in the needle valve, what should be done?

When a groove is found in the needle valve, it is crucial to replace both the needle and the seat. This approach is necessary because the groove indicates wear or damage that can affect the seal and functionality of the valve. If the needle is worn or grooved, it may not close off the flow of fuel properly, leading to leaks or performance issues. However, the seat can also be worn or damaged in conjunction with the needle, which can exacerbate the problem and prevent a proper seal. By replacing both components, you ensure that the new needle can effectively seat against a smooth and undamaged surface, restoring proper operation and efficiency to the mechanism.

Simply replacing one without the other could lead to continued problems, as the new needle may not function correctly against a damaged seat or vice versa. Thus, replacing both ensures a complete and reliable repair.