Here is a post when I was having the valve keeper problem. You will notice that I said this was one of the 70's that had weak valve spring and they replace them. Then the person said we don't have any record of your engine. Hummmm!!! they did when they replaced the valve springs. They also sent in the return engine a break down of WOT and Idle speed, said every thing checked OK

To late Gray Beard. I lost the ***** spring. If flew outside the bag. Guess I will be sending it to Magnum Service (Hobby People) I don't kown what caused the valves to set up. I have not used the engine for almost a year. It is only (maybe) 2 years old. It was going on my Spot on 50. Just have to wait until they do what they are going to do. This was one of the 70's that had weak valve springs and they replaced them. They are good people. Have a Happy New Year.
Gene