I get a bit worried when people use words like "going to town" and "give it a good scrub". Carbs are intricate assemblies with jets that are precision parts. The carb cleaner above is ideal. They are usually a strong solvent like acetone. (brake cleaner is similar but a slightly different solvent). The inside of th ecarb often looks realtivly clean, th ecleaner will remove any sludge, varnish and water. Take care with carbs. Clean the outside before dismantling them. Try to remove the float bowl with e card the right way up - tricky but it prevents dirt form the float bowl falling into the jets. Plus you will see how much dirt is in the float bowl. Remove the jets and clean them with the cleaner. Check all the small holes are clear, look through them to a light (not too bright). Don't be tempted to use wire to remove any blockages, use something plastic like a bristle form a brush, the jets are usually brass and easily damaged. Check the float is not leaking, shake it to see if it has petrol inside. Check the float valve seat for excessive wear, if worn you will need to replace it,