I put the GYT-R insert in the day I bought the my new WR450F, along with the YZF throttle stop. It wasn't until I looked at it closely when I went to wash the bike that I noticed that one of the 3 'barrels' inside the insert was half blocked with extra welding material, and one of the other barrels was about 25% covered. By my rough estimate, about 20-25% of the total opening area was covered. I took my tough drill bit set out (that metal is HARD), flipped the inert over and matched the drill bits to each barrel size. You can take the outer trim ring off if you want but I didn't. Stand the insert up in a machinist's vice (or regular vise if you are using a hand drill), lube up the area and use your drill press to slowly drill through the extra material on each barrel. I also used a fine rattail file on the input end to smooth each barrel's input edge. The same file was used to finish the output ends of each barrel. Might as well get the most out of this piece! Jim PS Love the bike... what power!