Difficult to get inside of these things, due to the coloured quadrants that adjust the mixture - effectively those plastic ends have to be broken off to remove the needles themselves. The slight adjustment given at those quadrants is unlikely to make much difference.
I think this carb is by Zama, and its a C1U - H46A.
These numbers will be stamped on somewhere.
Now then - these carbs are available from Amazon at around £15, and considering it's age, I'd replace it.....the diaphragms themselves would actually cost more.
John