HMF Jet Kit | Honda TRX 400EX 1999 - 2014 Re-jetting will provide the best air/fuel ratio after installing an HMF exhaust. OEM jets. Keihin jets for Keihin carburetors and Mikuni jets for Mikuni carburetors. Baseline jetting as well as smaller and larger jets included to accommodate changes in altitude or humidity. Bikes must be jetted for valid exhaust warranties. Included: Individual Keihin Hex Jet: 152, 160, 165, 170, 180, 190 and 42 Pilot