Originally Posted by EdwardN

Hmm, heven't been here for while.
Well, no one is answered right for nature of that hole.
I will try to help:
Look on the second picture and you will see there ie a grove right behind front bearing and this grove is pretty much hydraulic look to keep case hermetically sealed (when cranck is running oil in that griove create sort of barier. But over the time there is a lot of oil collecting and it will start leaking through the front bearing. So prevent oil leaking from front bearing, designers needs to have hole which is going from carburatortor area (which always have negative pressure) to that grove (if you remove carb you will see that end of hole). To make it manufacturable (it is not possible to make internal hole), you will need to drill the hole from front bearing through grove up to undrneath of carb. But now to make it work as sucking pump, the front end of hole needs to be blocked, so it will not suck oil/air from front bearing. Then hole is blocked on the very end of it on bearing side up to the grove. Now you have perfect chanel from carb area with negative pressure to the grove and all extra oil will be back to motor. You need to block the hole as I explaned above, or do whatever you want to.

Have fun.