S600-26 Black Tip Not Working

A landlord from Champaign says:
August 23, 2018
Hello,

I recently bought a set of 2600-26 spiral window balances for a large set of windows (older double hung) and unfortunately the Black Tip models do not have enough "pressure" to hold the window up. I was informed that these are the highest grade tip and that I may need to purchase another model/series. Any information is greatly appreciated.
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Tom from SWISCO responded:
August 28, 2018

The black tip option is indeed the strongest we carry. What is the weight of your sash? Please be as precise as possible, down to the ounce. Can you also confirm that the S600-26 is what you need? It's important to make sure that the diameter of the tube is 5/8" or 9/16". Finally, how many times did you wind the spiral before you installed it?
A landlord from Champaign says:
September 5, 2018
I do not believe our technician wound the spiral before installing. I purchased a winding tool and will check back when confirmed.
26" Series 600 Spiral Tilt Window Balance
26" Series 600 Spiral Tilt Window Balance
S600-26
$9.05
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