R50 jetting

[dardaris2725]

I've got a pair of clean, rebuilt, lever top carbs I'm going to put on my '59 R50 while I refurbish the originals. While looking over what internals were fitted thru the years, I noticed at some time the R50 main jet jumped from a 105 to a 120 in the later carbs, while the other components remained the same. What were the changes that necessitated the larger main jet?
Must be some increase in breathing, and a little power.

[schrader7032]

Looks like the change was only in the last iteration of the carbs...service bulletin dated 7/67 indicates when the change happened. Seems to be associated with the use of the new air cleaner and a Micro-star filter element...can't say as I know what that looks like. But they cite increase air flow with the new filter thus the increase in the main jet.

In my mind, this only comes into play when you begin to approach wide open throttle where the gas flows completely through the main jet. Before that, the needle and its jet controls the amount of fuel. There is some cross over and the Bing book suggests that begins around 60% of full throttle while the effect of the needle goes out to 80% throttle. Still, I wouldn't think that the main jet really helps that much until well past 60%.