I currently have a 99 yz400f with WB E series exhaust. I have the quiet core insert and five disks but I am going to be enetering a enduro in March and I need it to be under 96db's. I dont think the e series is going to get it done. I am considering the original version of the FMF Q series to put on the bike to get me through the race with out breaking the bank. Problem is I have heard of some 426 guys having trouble jetting there bikes for this exhaust. any body had trouble with the original Q and jetteing on there yzf's? PS: If anybody is interested in The E series muffler and WB head pipe both in excellent shape email me they are for sale or trade for a stock 400/426 sysem, they do me no good in California.