Dear Ralph, A friend is turbocharging a ZRT 800 and we might need a bit more fuel from the power jets than what we’re...

Dear Ralph,
A friend is turbocharging a ZRT 800 and we might need a bit more fuel from the power jets than what we’re using. What do the numbers on Mikuni jets (main and power) really indicate? Does it have anything to do with hole diameter, flow rate in cc’s over time, or something else? I have access to a machine shop so drill accuracy and hole size aren’t an issue.

Lee Sledjeski

As far as I know, the Mikuni jet numbers are definately an orfice size indicator. With a numbered set of drill bits you could gauge the difference from one size to the next and “make your own” to whatever size you desire. I would recomend that you use a belt sander or something similar to remove the “old” jet size number to avoid any confusion and mark your new jets in a manner so you know what you have.

I can tell you that when it comes to non-Mikuni jets that the sizing is not as accurate as what Mikuni makes. For example, a non-Mikuni jet size 350 may not nesecarrily be 1 size bigger than the Mikuni 340. I’ve seen it where the 350 in question acts more like a 330 Mikuni. The moral of the story here is to stick to genuine (Mikuni or Kehin) jets for general tuning. The Mikuni ones always have the little emblem or insignia stamped on them so you know that they’re the real McCoy.

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