The other day I was trying to fettle the #4 because the shavings were clogging up in the mouth, something that never happened before. I first lapped the chipbreaker on the back surface so that it seated flush with blade, and then I stropped the front edge to allow shavings to flow over unhindered. This didn't work.
I then tried moving the frog forwards and backwards-this didn't work either. Too far forward & the plane mouth closed up, and too far backwards and I couldn't adjust the blade downwards-the adjustment screw reached its limit.
There was only one thing left to do. I moved the chipbreaker further back along the blade, leaving a much larger gap. This seemed to work fine, even though I've read that the gap has to be much smaller. Maybe Stanley planes were not designed to take other blades?
Aside: In the background of the 1st picture is a Paul Sellers-inspired hand tool applicator. take home-use machine (inorganic) oil only!