Yamaha Bass Clarinet Mouthpiece 4C

I bought this mouthpiece as a replacement for that on my relatively cheap Chinese instrument (Locto) in the hope that it would improve the tone. The manufacturing quality is the usual high standard of Yamaha, however in order to even fit it I had to remove a large amount of the cork seal, it seems all bass clarinets are equal but some are more equal than others! Question is does this nullify the guarantee? When fitted the performance (or mine) was no different, but as a total beginner on the bass clarinet maybe this doesn't count as a valid review and only time will tell and if I ever get to use it. I gather that different mouthpieces have different gaps but there doesn't seem to be a way of making easy comparisons of the effect of choosing a different gap, any feedback would be appreciated.