I have a WhistleStop-tweaked Clarke Original which plays flat. Is there a way I can tune it up? If I grind down the end a little, will that affect only the bell tone, or the other notes as well (which is what I’d like, because all notes are uniformly flat on it)?
I’d dearly love to fix this whistle because I love the tone.
jomac
Grinding down the bore end will only affect the bell note for the most part(it will affect the spacing between the holes as well).
To correct overall flat pitch,the bore must be shortened at the other end. To be specific,reduction of the bore between the voicing and the first(highest)hole.
Because this is a “Clarke”,I assume it is “non-tunable”? If so,I suggest placing a wad of putty/beeswax/etc. below the voicing window and up against the bottom of the inner fipple plug face. This will reduce the internal volume and sharpen the overall pitch.
If this “wad” is made of beeswax or other waxy putty,you can add to or subtract from it until you acquire perfect pitch(Thomas controls an outburst of laughter). If this harmless “tweak” is successful,you can make it more permanent later.
I hope others will chime in with their suggestions too.The object is to make this instrument usable, so more options from more experienced people will give you the best choice for YOU. 
Thomas Hastay.
If you mean the Whistle Shop, I just ordered a tweaked Clarke Original from Thom and mentioned your post. He said that if I had any issues he would make them right.
If you got it from there just contact him and he will work it out.