On classic pedal mopeds (not scooters), “won’t start” almost always fails one of three tests — in this order: spark → fuel → compression. Jumping to jets, a pipe, or a top-end kit before those three wastes money and can hide a seize risk.

Work the order — don’t skip

  1. Spark — pull the plug, ground the threads to the head, boot on, pedal or kick in shade. You want a crisp blue snap. No spark → stop and follow no spark.
  2. Fuel — petcock on, fresh fuel, bowl/drain shows liquid not varnish. Premix bikes: correct ratio via oil mix. Wet plug + strong fuel smell → treat as flood (flooded Bing on Puch).
  3. Compression — firm bounce on the pedal/kick. Soft feel = rings, head gasket, or worn bore. Guides agree: compare warm compression to a known-good runner — no universal PSI religion. Tomos and Honda guides flag roughly below ~90 PSI warm as a top-end conversation on a healthy gauge — still verify for your engine.

1. Spark first (platform notes)

  • Puch: From the Puch Maxi guide — points gap commonly 0.016″–0.018″ when fully open; plug often NGK B6HS at 0.020″–0.024″ on points bikes. Clean points, oil the felt pad, lube the flywheel cam before blaming the Bing.
  • Tomos: Plug often BR6HS (CDI) or B6HS (points) per the Tomos guide; gap about 0.8 mm on CDI bikes; points gap 0.35–0.45 mm on pre-CDI. The maintenance hub also lists B7HS on some Tomos/Honda service notes — trust your manual and platform guide over a generic list.
  • Honda Express / Hobbit: Still needs spark and a working oil pump before you blame the carb — Express guide and oil pump. Do not treat a stock Express like a premix Maxi.

2. Fuel delivery checklist

  • Petcock on; fresh fuel. Stale tank varnish kills more starts than “bad jets.”
  • Premix platforms (most US Puch / Tomos): stock starting ratio often 50:1 — see two-stroke oil. Richer for break-in or kits is covered there as a starting point.
  • Do not premix a stock Express as a substitute for fixing injection.
  • Crack the Bing / SHA / PHVA bowl or drain: fuel should appear, not sludge.
  • If the plug is wet and the jug smells flooded: dry or swap the plug, hold throttle open outdoors, clear the cylinder — then fix the needle/seat if it keeps overflowing.

3. Compression (last of the big three)

Soft pedal bounce or low warm gauge reading points at rings, head gasket, or bore wear. The Tomos and Honda guides both use “compare to a known-good runner” as the real standard; the ~90 PSI warm flag is a conversation starter, not a law.

Platform forks (after spark / fuel / compression are sane)

  • Puch Maxi E50 / ZA50 — Bing, centrifugal or 2-speed auto, premix on most US bikes. HP class (1 / 1.5 / 2) changes jets and restrictions — don’t copy a stranger’s main jet.
  • Tomos A35 / A55 — SHA (A35) or PHVA (A55), chain + 2-speed auto, gearbox ATF separate from premix.
  • Honda Express / Hobbit — oil injection; clutch/ramp wear is a separate failure mode from “won’t fire.”
  • Carb jetting — only after spark, fuel, and compression are sane. Plug-chop at WOT; change one jet size at a time.
  • Engine revs but bike won’t pull → clutch slip. Starts then falls on tip-in → bogging.

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