I would do it every two to three years. I just did one a month ago. Was rebuilt 5 years ago. Just recently, engine was hard starting, rough idle, etc. After I did the rebuild, engine starts right up, idle mixtures perfect. When you shut down and let car sit for a few hours, go back and bump the starter, engine starts right up without even pumping the gas. Very happy now. I think I'll do more frequent rebuilds now.
