MOPED ARMY

thin air means smaller jet, what's the rest of the setup - that's obviously critical.

Even still we could only give you a best guess, you'll need to tune it yourself. Take whatever jet you have and try one larger and one smaller and see if it gets better or worse. does it bog when you open the throttle, does it stutter and 4 stroke at wide open?

You can also to some extendt rely on "plug chops", if you take the plug out and it's bone white - upjet. drippy black, downjet. this method can be fairly subjective though and only reliable to identify extreme problems. beter to tune by how it performs.