About 25 years ago I had my carbs painted with a 2 component varnish that has held up well until now. The misery with peeling off at the bottom started a few years ago when the normal petrol here in Holland was mixed with 5% ethanol (now it is 10%). No owner of a classic car or motorcycle still uses this kind of petrol, but luckily the ethanol-free petrol (98) is still widely available (Shell V Power and BP Ultimate). To clean up my carbs I got a tip from a Dutch clubmember and professional restorer, Motip Wheelspray Steel Wheel 04010, which is supposed to be a perfect Amal carb tint and is for sale here on the continent in a regular spraycan (instead of per litre or gallon) for the price of 8 Euros.