From what I can see, it is the same.

I don't think so.
I think you will find the 12005 is M12 and the 10004 is M10.
90171 12005 is superseded 90171 12039.
 

Thanks Pete I'll have a look at that alternative part number, cheers

Hello again can someone confirm the pitch so castle nut M12 (is it 1.25p 1.50p or 1.75p) cheers if you know the answer

Hello again, Winter has come and gone and Spring hurtled in with a big chunk of warm sunshine.
- Still havent replaced the castle nut
- I have a very rattly piston or a knocking pinging issue, currently running BR7ES (as provided by PO) which could be the issue (though its burning a very nice coffee / milk chocolate brown) so will experiment with a BR8ES
- tuned the oil pump setting and throttle play and it seems to be a tad smoother and less oily at the pipe, seems like less white smoke too
- still managed to put in a solid 4 hours of almost non stop riding

Good to see ya out there doing it. Things i only dream about these days. & when we did all that it was on old & heavy British 500cc bikes.

Yep it was a blast, I always need more! Gave the arms and legs a good workout! Am trying to work through airfilter, snorkel and plugs to eliminate this top end rattling. Again need another ride out to see where I'm at, but with a lot of throttle control and gear changing was able to keep the noise down. Sure these old air cooled Yam's are light and nimble, can't really want for anything else. Just can't beat a good long sunny day in the woods, can't get enough right now

imgur.com/Y6jTBoS

Really need to find some new trails and routes. Nearby is all short and too much road, the good trails are far, so I need something for a local fix