Surpass 70
 

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

Surpass 70
 

First off, you might want to check the rocker arm to valve clearances. This is detailed in the engine instructions.

Having the engine go from rich to lean to rich to lean also indicates some kind of fuel system problem. You may need to check it to make sure there are no leaks or kinks in the fuel tank and lines.

Make sure your fuel is absolutely fresh. If you're running fuel that's been sitting for a few years, it can have deteriorated, especially if it's been opened at some time.

The valves may be sticking from congealed fuel residue. The only way to fix that is to disassemble the engine and clean them. The same goes for the piston/ring fit. The ring may be stuck in the ring groove and is causing problems. Again, only disassembly and cleaning will fix the problem.