The Puch Maxi is a 49cc two-stroke with pedals — stock roughly 1–2 hp and ~30 mph, with well-built examples reaching 45+ mph after tuning. This guide covers US Maxi/Newport bikes, not scooter CVT advice.

Know Your Engine First

  • E50 — one-speed engine with a centrifugal clutch (typically 2-shoe) in the clutch bell. Most common US Maxi/Newport engine. The left-hand lever engages the clutch for pedal starting; once running, the clutch grabs automatically by RPM.
  • ZA50 — automatic two-speed with internal centrifugal clutches. No manual shift — gears engage by RPM. Rectangular transmission cover vs the E50. Some versions had oil injection. Different internal gearing, transmission fluid, and clutch service than E50.
  • Both are piston-ported stock — no reed cage from the factory. Reed valves are an aftermarket mod requiring case work.
  • Stock carb is usually a Bing 14/12 or 15/15 depending on year and market — jet size varies by carb part number and HP rating, not just bore size (see jetting guide).
  • HP ratings — 1 HP, 1.5 HP, and 2 HP versions correspond to roughly 20, 25, and 30 mph classes from the factory. One-horsepower bikes add extra intake port restriction, thick head gaskets, and smaller main jets.

Stage 1: Baseline & Free Gains

  1. Compression test — E50 baseline varies; tired engines may read ~90–110 PSI, healthy builds higher. Compare to a known good runner.
  2. Points & timing — Stock points gap is typically 0.014". Ignition timing on an E50 should land around 14–17.5° BTDC (roughly 14–17.5 mm on the flywheel rim with a timing light). Kitted aluminum cylinders often want 14–14.5° to stay cool at WOT. Setting timing by ear or by when points first crack open is inaccurate — use a timing light and piston stop for TDC.
  3. Spark plug — Often B6HS or equivalent; gap commonly 0.020"–0.024" on points bikes.
  4. Exhaust restriction — Remove baffle/restrictor ring if present. Pair with jetting — never open exhaust without checking plug color.
  5. Intake restrictor disc — Many stock intakes have a disc; removing it increases flow and requires richer jetting.
Ad — In-Article

Stage 2: Centrifugal Clutch Tuning

E50: tune clutch shoes and springs inside the bell — not scooter roller weights, and not a Peugeot variator. ZA50: tune shift timing via clutch weight, springs, and transmission fluid. Common E50 notes:

  • Stock grab RPM is often too low for tuned setups — blue springs are a common minimum for performance builds.
  • Shoe weight matters quadratically — lighten carefully; never under ~55g per shoe or you risk slip instead of grab.
  • With blue springs, builders have tuned grab to ~5800 RPM by balancing shoe weight and spring tension.
  • Replace glazed/old clutch lining — hardened shoes slip badly.
  • High-RPM builds may need pivot braces to stop bending.

Stage 3: Pipe, Jetting & Air

  1. Performance exhaust — Bi-Turbo, Tecno Circuit, etc. Match pipe to cylinder and jet accordingly.
  2. Jet by plug chop — After any airflow change, read the plug at WOT. Stock Bing 15/15 often starts around #52 main — see jetting guide for mod steps.
  3. Air filter — Pod or modified airbox — always jet to match.

Stage 4: Big Bore Kits

70cc kits (Airsal, Athena, etc.) are the largest gain. Expect port matching, pipe, jetting, and often clutch work — 40+ mph is achievable but not bolt-on and forget.

  • Full-circle cranks help certain builds but are not mandatory for every kit.
  • Reed kits are a separate project — case work required; not a drop-in Stage 2 part.

Oil Mix

Stock Puch often ran 50:1 with quality 2-stroke oil. Break-in and kitted builds often run richer (32:1–40:1). See our oil mix chart.

More on this site