Old windows are problematic, they look right but often they don’t work right. However. while replacement windows may work well, vinyl ones look quite out of place on an old house, and attractive new wooden sashes are expensive!! Now you can preserve the original windows and maintain the character of your home. Improve them with vinyl jambliners which make sash slide easily, stay open in any position, and allows both sash to tilt for easy cleaning and maintenance.
WHAT IS WRONG WITH THE SASH WEIGHT SYSTEM?
This turn of the century  technology is simply obsolete now. In order for sash weight windows to slide up and down easily they must be loose, side to side, especially if the opening is out of square. There is no effective way to weather-strip them and still have them work. Try this on your window- grasp the bottom sash in the center of the meeting rail and pull toward you and then side to side feel the play? that is what makes them move freely and what allows the wind to rattle the windows!.
As the sash go up and down they rub on the parting bead [the piece in the jamb that separates the top from the bottom sash] and on the interior and exterior stops. This creates paint dust- often LEAD PAINT DUST which is a known hazard if ingested.
The sash weight pockets are a large [approx. 3″x3″x window height] space that cannot be effectively insulated and have the window still work.The sash do not tilt and removing them means removing the interior stops, removing the chain or sash cord. etc. this makes it difficult or impossible to glaze and /or paint a 3rd floor or otherwise hard to get to window.
This new system works on all double hung windows whether sash weight or balances, provided the side stile of the window is at least 1 3/4″ wide.