Hacksaw a slice of the end off, there is lots of threads & the bung is thick. Then put a hacksaw cut across it to make a screw driver slot. If you pull it apart you can then turn the bung in instead of out which will then let you clean up the first couple of threads in the housing.

Alternately, drill a hole in the middle large enough for a smallish screw driver & then lean out the whole range. Try an 1/8 of a turn in. Ideally, if you turn the centre screw in an 1/8 of a turn you should turn the full load bung the same amount out to maintain the same mixture at full throttle, but make it leaner every where else. You can gain part throttle fuel economy by leaning the mixture out until you find that you have to push the accelerator down further to maintain the same speed. It's a complicated concept to put in to words, but it's one of the reasons that diesels are more economical.