This demonstration guide answers one field question about a jet that was right at sea level and lean at altitude. Measurements come before parts, and the notes are not a generic equipment FAQ.
Diagnose before replacing parts
Start with plug color after a loaded run at local elevation. That reading separates a jet that was right at sea level and lean at altitude from adjacent faults that share the same complaint.
If the measurement is out of spec, treat the main jet as the primary path. If it is in spec, do not replace the main jet just to complete a parts list.
Repair the failed system
The usual correction is the main jet, installed to the documented spec for this complaint.
A demonstration shop records the finding so the next technician is not repeating a guess about a jet that was right at sea level and lean at altitude.
Stop before you make it worse
Do not drilling the jet because the engine "wants more fuel". That shortcut hides the original measurement and creates a second failure.
If the machine still fails after the main jet is corrected, convert the visit to a broader diagnosis rather than stacking parts.
Written and published by Ridgeline Small Engine.