Yes, I've done this a number of times to a variety of chain driven mopeds and motorcycles. On motorcycles it's easier to put on a larger countershaft sprocket, you don't have to remove the rear wheel. Try a smaller rear sprocet, you'll need to shorten the chain ( save the small section you remove, if it doesn't perform the way you like it, you'll have it to reinstall it ) and possibly drill holes in the rear sprocket to get it to line up with your hub. Make sure the dish of the new sprocket is the same as the old one so your chain lines up. Experiment around, if you don't like the way it pulls of the line, go to a slightly larger sprocket. Remember, if you save your old sprocket, you can always go back to the original setup.