Unscrew the spark plug cap off. Take a good pair of clippers and chop it off. Leave some extra room just in case. Screw spark plug cap back on.
This won't change anything performance wise.
About the dying at full throttle, that very thing happened to me today. It was very frustrating because many things can cause it and they are very generic problems. The causes can be:
Bad Ignition Timing
Misc. Electrical Problems
Improper Gas/Air Ratio
After changing the carburetor and electrical system, I got rid of causes 1 through 3. I highly doubted that it was Improper Gas/Air Ratio because that just doesn't change over night but it had. I upjetted and it worked.
For you, though, I bet it's a dirty carburetor. Please refer to Fred's Guide to Repairing Mopeds. It's in the articles section of this site.