TOPIC:

Are original factory Mikuni 5DL31 needles used in a Mikuni VM24 carb set identical to after market needles, that you find in kits, stamped Y63? Same taper, length etc? I'm assuming they are, but I'd like positive confirmation please.

The numbers you refer to are call badge numbers. 5DL31 jet needles are common to a variety of Mikuni VM series carbs where the Y53 number is a Keyster number; a manufacturer of carb rebuild kits. You will have to measure the length and taper to be sure. To measure the taper, start 10mm from the pointed tip and make measurements at 10mm and every 10mm above that. If the diameters are the same, as well as the length, the jet needles can be considered the same.