Skeeter_Fogger Posted July 6, 2020 My Mikuni VM16SC calls for a #115 main jet. The one in it is 0.025" diameter. It is too lean but I have not been able find what diameter a #115 jet is. Can anyone tell me or steer me to a # vs diameter chart? Share this post Link to post Share on other sites
William1 My Rides (2) Posted July 6, 2020 Jet number is based on flow rate, not absolute orifice. While you could ream one out, why not just call JetsRUs or JD jetting and buy a couple of properly marked different sizes? Share this post Link to post Share on other sites
Skeeter_Fogger Posted July 6, 2020 You are correct in your assumption that my jet is not part marked. I have a set of ten jets on order. Meanwhile, a #72 drill is .025", #71 is .026" and #70 is 0.028" diameter for a 8 and 25% area increase. I might be able to use a pin gauge to broach to 0.027". This approach would be counter to Gordon Jennings "start with NO main jet" approach. I realize that the jet # represents a flow rate not an orifice diameter, I'd just like to get a feel for where I am at. I suspect someone jetted the bike for high altitude. Share this post Link to post Share on other sites
William1 My Rides (2) Posted July 6, 2020 1 hour ago, Skeeter_Fogger said: You are correct in your assumption that my jet is not part marked. I have a set of ten jets on order. Meanwhile, a #72 drill is .025", #71 is .026" and #70 is 0.028" diameter for a 8 and 25% area increase. I might be able to use a pin gauge to broach to 0.027". This approach would be counter to Gordon Jennings "start with NO main jet" approach. I realize that the jet # represents a flow rate not an orifice diameter, I'd just like to get a feel for where I am at. I suspect someone jetted the bike for high altitude. Being you do not have 'all jet sizes' (few do have a full spectrum) and Jennings is starting with the concept of 'complete unknown'. You have a jet the sort of works and you feel it is lean. So a tiny enlargement for experimentation while you wait on USPS is OK. My concern is those that 'wing it' because they refuse to get the right jet. Then someone come along, sees the jet size in the bike and replaces it with one with the same marking, which at this point would be too lean and then cooks the engine. I seem to recall someone did make a chart in this section of TT years ago but I do not know if it was Mikuni or Keihin. I'll see if I can find you a cross reference. Share this post Link to post Share on other sites
Randy K Posted July 6, 2020 Here you go from a good source https://www.jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm 1 Share this post Link to post Share on other sites
