Saving Old Seagulls

hi everyone,could you please help with suggestions regarding fuel mixture issue.....
after 10>15 mins running my forty richens it's mixture by itself...causing it to eventually choke itself up and stop..... on investigation i have found that the small adjuster screw on top of the needle winds itself upwards.... further examination revealed that the small nylon pin in the middle of the mixture screw is worn!
can this be replaced or is there another solution to this problem.
all suggestions will be greatly received.... many thanks.

Did you try opening the slot on the screw slightly? Or can you find a piece of nylon same size, but that will engage the threads in the throttle piston slightly?

i think that the nylon pin should be slightly tight as it is engaged with the thread in the piston but it doesn't seem to have any resistance to it...
could it be possible that the spring under the needle is weak as well???
is this is so can they be replaced with slightly stiffer ones!

PROBLEM SOLVED!!!!!!!
after searching around i pushed the old piece of nylon out of the adjuster screw and replaced it with a piece of 2mm grass strimmer nylon wire cut slightly longer than the screw diameter.......nice snug fit...
PROBLEM SOLVED...RUNS PERFECT ONCE AGAIN...