| With some of the cheap horns going around today (and some of the big name brands have some cheap stuff on them) the metalurgy (sorry about the spelling) is wrong in the alloy used to make the valves. If the alloy has too much tin in it, it will "gaul" with the casing. (When you rub like metals together they stick to each other) The evidence of this is brown places on the valves. If this is the case, you can take a rag and some lava soap an polish the brown spots off the valve. Of course the problem will return with time.
The Jupiter corporation admitted this problem, and has sent out replacement valves to all who have Jupiter horns with this problem. This has really made me a fan of Jupiter. The had a problem, admitted it, and took care of it. I can name at least 2 major inst. makers who have the same problem, but are denying it and not taking care of their customers.
But like Rob said, the last thing you want to do is actually lap a valve. Once you take off too much metal, it is really hard to put it back, and not cost effective.
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"Music is a fire in your belly that has to come out of your mouth, so you'd better put a horn in the way before someone gets hurt" (paraphrase of Bleeding Gums Murphy) |