I have a new low C bass clarinet that has a flat low C#. The low C and low D are fine. The low C# is ~30 cents flat. As a test, I pulled the bell out on the cork about 1/16". This made the low C and C# ~13 cents flatter. So to make the low C# 30 cents sharper, I figure the tone hole on the bell needs to be located 1/8" or a little more higher than it is. The key needs to be altered to work at that location too. Alternatively, the body length could be made 1/8" shorter but then something needs to be done to lower the low C pitch back down. Like the bell bore made smaller. Any thoughts from instrument repair people?