Has it always surged in WOT(wide open throttle)? If not then what is happening is you are not getting enough fuel what you are a full throttle. This can be from different things but it all has to do with fuel delivery.
1. Clean out your fuel tank. Make sure nothing is in it. Use that gaS in your car or truck along with the fuel from your gas can.
2. Clean your gas can as well.
3. Replace all fuel line with ethanol fuel line.
4. Clean your carb. Lots of videos on how to clean your carb on youtube.
Report back and let us know how it worked. It is almost always your carb being dirty but with ethanol fuels now your fuel system could be causing the problem with the carb being dirty.