Hi Nath, thanks for the reply.
The main nozzle is the only bit I haven't been able to remove, it looks like someone before me has had a go and even though I modified a screwdriver tip to fit nicely in the nozzle slot I haven't done it any good either.
I've double checked the main needle spec, the Briggs & Stratton document that has exploded views of all the parts says the main needle is Part No. 396568. When I first got the mower it had the needle with the green seal so I replaced it with the correct one.
I've ordered a new carby off Ebay, aside from the nozzle issue the existing carby has quite a bit of surface rust inside the fuel bowl and on the choke baffle plate. I think given the damage to the main nozzle my most likely option will be to use a screw extractor to remove it so once I factor in the cost of a new nozzle I might as well spend the $60 and hopefully have a replacement that's good enough to be able to tune properly.
I'll remove the old carby when I have a minute because as well as trying to get the main nozzle out I also want to check for play in the linkages as per your suggestion above.
I'll post back on my progress in case anyone is interested in reading about me muddle my way through this.
