Thanks for the links Rodeobob. I was typing stuff into the computer all day trying to find links and you put up two. Cheers.
I ended up buying a second hand carb which is close to mint. I cleaned the external grime, put it on and added a fuel filter this time and it fired right up. It was a quick tune due to the time of day but I'll have a better play tomorrow.
It idled beautifully and ran out to full revs without a cough. There was no backfiring on deceleration too which was good.
Once I removed the air cleaner housing and the intake manifold on the old carb I found it had quite a lot of corrosion. I didn't think that fuel would do that. Perhaps it had some water in it at some stage during it's storage??
If I can get the camera working I'll take some pics.
The only small issue I have to work out is that the new carb must have run a linkage choke lever. The choke is spring loaded. The old choke was a direct mounted lever.
The part number that you require for a new genuine carby is 632351 and cost around $160.00 but it depends on your budget if you want to go for a new one or a oregon one.