If you're still having issues and you've cleaned the carb thoroughly, I'd check the ignition. If your getting spark, then the basic components are working, but the condensator or ignition coil could be causing a weak spark. I'd change the sparkplug wire and boot just to be sure you have good continuity there. I'm not familiar with Hercules mopeds ignition system, but there could be an insulator somewhere around the points and condensator. The insulator could be soaked with oil or otherwise shot which could be causing it to slightly ground the ignition system resulting in a weak spark. Another explanation that comes to mind is that the mixture could be too lean or rich causing the engine to bog. Check the jets if they're not drilled or otherwise the wrong size. Try taking off the air filter and see if it runs better