My engine keeps surging

I have cleand it what is berryman b12

google it or ask for it at a parts house. Its a fuel additive that generally pushes enough crud out of and through an engine to get it working, it generally does a decent job on lawn mowers but will run terrible while its in there so you might have encourage it with a can of carb cleaner (NOT ether) but it will cover a lot of sins.

You might also have a look at your air filter. Those small engines surge like that when they're struggling to run for one reason or another, typically because they're not getting enough gas.

I assume the problem you're having is that the engine nearly chokes out then revs up just to drop back down?

If the problem is the engine just trying to run away, its probably getting too much gas, in which case the problem is still with the carburetor but ignore everything I've said so far, it won't work. It may be stuck open, theres a little spring that likes to break and a few other things that could be going on.