Hirth Brain
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Lean misfire above 4500 RPM — 3503
Fixed
550cc
Updated 2026-05-18
Overview
Hypotheses
2
Notes
1
Collaborate
Possible Causes
None of these? →
#1
Defective PTO-side crank seal (batch 26-A14)
88%
· works
#2
Cracked reed valve petal
51%
· fails
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