That's pretty low gearing unless you're running absurdly tall tires. The transmission shifts when the idler gear shaft reaches a certain RPM...not the engine.
For example, on my XL (Terra Pins, factory 16/52 gearing) I had to disassemble the tranny several times to loosen the second gear clutch pawl before it would finally shift. This was after I had the engine broken in well and running top revs.
I had it working nicely, even shifting a bit too early, and yesterday I tried 14/51 gearing and she would *barely* shift into second and only then sporadically. The tranny just wasn't reaching the required RPM before the engine was running out of breath. Today I changed to a 15 tooth CB and things are working again.
So yes, if your engine is running a good tune and reaching normal high revs like it should, you are going to have to adjust your shift points starting with second gear as already stated.