Bogging (falls on tip-in) and four-stroking (irregular miss at part throttle) are mixture / air-leak problems until proven otherwise. Do not copy main jets from strangers — the jetting guide exists for a reason. Classic pedal mopeds only; Bing numbers are not SHA numbers.

Before you touch jets

  • Air filter not oil-soaked or collapsed.
  • Intake boot cracks / loose manifold bolts (false air → lean risk / seize).
  • Fresh fuel and correct oil approach (premix vs Honda injection).
  • Spark quality verified (no spark).
  • On Tomos: dirty SHA / PHVA and choke-cable issues are called out in the Tomos guide as common off-the-line bog causes — clean and verify before chasing mains.

Plug-chop method (site standard)

From carb jetting: install a fresh plug, ride 1–2 miles at WOT, kill at speed (don’t idle home). Read the center insulator — tan/light brown close; white/chalky lean; oily/black rich. Change one jet size at a time, then re-test.

Starting points (not gospel) — cite your carb stamp

  • Puch Bing: Stock mains vary by HP class and Bing part number. The jetting guide lists example stock mains by carb code (e.g. 1 HP / 1.5 HP / 2 HP families). The Puch guide’s factory 1.5→2 HP bulletin example includes main #50 → #56 among other required changes (manifold, slide, needle jet, filter pipe, exhaust pattern) — not “bigger jet and hope.” See Puch Maxi guide + jetting.
  • Tomos SHA 14/12 (A35): often around #53 main stock starting point; A55 PHVA around #55 main / #25 pilot — Tomos guide. SHA numbers are not Bing numbers.
  • After pipe, pod filter, or kit: expect re-jet — build paths. Never open the exhaust without checking jetting.

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