I have a surpass 70 that I've had for many years and it has worked flawlessly. I haven't used it for about a year and decided to put it on a Pizazz that I put together. The engine starts excellent Idles great. As soon as it gets to the top end it leans the richens then leans back and forth as if the needle doesn't matter. I run power master 15% with 20% synthetic oil content. It has a brand new type F plug and I've reset the tappets and cleaned the carb to no avail. Somebody told me I might have burnt the valves how do I know for sure and what should I look for? If this isn't the problem what could it be?

Any help would be appreciated!
Thanks in advance