Did this question ever get properly answered?
I have struggled to rebuild the carburettor on my P50 which was very broken and corroded. It has taken me months to realise that there are two different carburettor types on the P50 and they take different jet sizes.
Most of the information on the internet is incorrect (nosurpise there).
I finally found a reliable source of information here;
From this I realised that my P50 has the B type carburettor and I needed a size 62 main jet and 35 idle jet.
Then I discovered that the correct main jet in size 62 is made of unobtainium. I had to saw a size 60 jet in half through the thread to give me just the emulsion tube which could be screwed home,and then saw down some 8mm Keihin jets to squeeze in on top.
That worked,surprisingly. And what I then found by experimentation was that mine only runs correctly on modern fuel with a size 65 jet. 62 is too weak, and 68 is too rich. These engines appear to be extremely sensitive to jet sizing.
The extreme sensitivity to jet sizing, and the erroneous information all over the internet explains why so many folks struggle to get these running correctly. But you will need a Dremel and patience to cut jets down in order to have a choice of sizes to try out!
Hope the information helps someone!