Tomos was among the last manufacturers building true mopeds before production ended. US buyers in 2026 are shopping used bikes — and you need to know which engine is on the frame. Slovenian-built (Yugoslavian originally) — not Italian.

A35 vs A55 — Don't Guess

On most US Tomos frames, digits 5–6 of the VIN identify the model. Common US examples:

  • A35 — Targa, Sprint TT, and related (VIN codes 44–49, 56, etc.). 1991–2006. Reed-valve cylinder, Dellorto SHA 14/12 carb, stock #53 main jet.
  • A55 — Revival and later US Tomos (VIN 26 = A55 Revival). Introduced 2003. Piston-ported nikasil cylinder, Dellorto PHVA 14 carb, stock #55 main / #25 pilot. A35 exhausts often need bending to fit A55 port angle.
  • A3 / A3N — older Sprint and classic-line engines. Parts overlap with A35 but not everything swaps.

Revival is A55, not A35. Streetmate is a separate Tomos model line — check your VIN and manual before ordering parts.

Drive Train — Chain, Not Belt

Tomos A35 and A55 use chain final drive and an automatic two-speed transmission inside the engine cases — not a scooter CVT, and not a belt to the rear wheel. Chain slack should be about 10 mm free play (up/down) and should be checked every 500 miles.

Transmission Oil (Gearbox)

Separate from premix fuel in the tank. Typical service notes:

  • A35 / A55 fluid: Type A (Dexron) or Type F automatic transmission fluid (ATF).
  • A35 change: drain bottom plug, fill through top until fluid weeps from the side level (Phillips) screw — go easy on that screw; it strips easily.
  • A55 capacity: about 10 fluid ounces (300 cc) if level screw is inaccessible.

Chain & Clutch Service

  1. Rear chain — clean, lube, adjust slack. Worn sprockets look hooked; replace as a set.
  2. Two-speed clutch — slipping, hanging in first, or slow shifts often trace to worn clutch pucks, wrong gearbox oil, or clutch shim issues.
  3. Reed block (A35) — leaky gaskets cause oily cases and weak low-end. A55 is piston-ported — different top-end parts.

Stock Specs Worth Knowing (A35)

  • 49cc, 38×43 mm bore/stroke, ~9.1:1 compression
  • Spark plug: NGK BR6HS (CDI) or B6HS (points)
  • Gap: 0.8 mm; points gap 0.35–0.45 mm on pre-CDI bikes

Common Problems

  • Dirty SHA / PHVA carb — bogging off the line; ultrasonic clean and verify choke cable.
  • Exhaust gasket blowout — loud exhaust leak; replace gasket, check studs.
  • Weak CDI / coil — test spark before throwing jets at it.
  • Rusty tank — replace fuel lines and inline filter after cleaning.

Compression & Buying Used

Compare warm compression to a known-good runner — no universal PSI rule. Below ~90 PSI on a warm engine is a top-end conversation. Check chain, sprockets, and that the trans shifts into second under load.

Performance & Build Paths

The A35 is a reed-valve engine with a two-speed automatic transmission — not a belt variator. Tuning follows reed, clutch, and jet logic, not roller weights.

  • Mild — Clean SHA (#53 main baseline), fresh reeds, ATF gearbox service, chain at ~10 mm slack. Expect 30–35 mph sorted.
  • Mid — 70cc kit with A35-fit pipe, stepped jetting, two-speed clutch puck and spring tune. 40–45 mph is realistic.
  • Wild — Ported cylinder, performance reeds, larger carb, clutch tuned for high-RPM second-gear pulls. 48–52+ mph with careful break-in.

Do not bolt an A35 pipe to an A55 without checking port angle (25° on A55). See the staged build article for parts logic and speed tables.

Tomos A35 — three build paths →

Oil Mix (Premix)

A35/A55 run premix in the fuel tank (unless someone removed a rare oil-injection setup). Most owners use 50:1 with quality synthetic 2-stroke oil. See oil mix chart.

More on this site

Service rhythm (A35 / A55)

Use this as a workshop habit list, not a warranty schedule. Your year and manual win when they disagree.

  • Every ride: kill switch works; no fuel smell on the tire; chain not hanging slack.
  • ~500 miles / monthly: chain clean + lube + ~10 mm free play; quick look at sprocket teeth for hooks.
  • Seasonal / after long sit: fresh premix, carb bowl drain if it sat with ethanol gas, gearbox ATF level check, plug color read.
  • After pipe or top-end work: recheck exhaust gasket leak and jet baseline before blaming the clutch.

Chain slap details live on the Tomos chain slap page — keep the 10 mm Tomos number; don’t borrow Puch’s midpoint free-play figure.

Carb, reeds, and air leaks

Stock A35 SHA 14/12 with a #53 main is the baseline this site uses. A55 PHVA 14 with #55 main / #25 pilot is a different carb family — jet charts are not interchangeable.

  1. Fix air leaks (intake boots, reed gasket on A35, exhaust gasket) before “going richer.”
  2. Clean the carb fully; a half-clean SHA still bogs off idle.
  3. Confirm choke cable frees fully — a stuck choke reads like a rich jet.
  4. Only then step jets. See carb jetting and bogging.

A35 reed blocks that weep oil into the cases usually need gasket and reed inspection, not a bigger main jet. A55 is piston-ported — different top-end parts path.

Two-speed behavior under load

The automatic two-speed lives in the cases. Premix oils the cylinder; ATF oils the gearbox. Mixing those jobs is how you get “mystery slip.”

  • Hangs in first / won’t pull second: check ATF level/type, clutch pucks, and shim stack before buying a pipe.
  • Slips under load in second: worn pucks or wrong fluid weight change engagement feel.
  • Loud slap, then surge: often chain/sprocket first — see clutch slip only after free play is right.

Buying a used Tomos — quick script

  1. Read VIN digits 5–6: A35 vs A55 (Revival) before you price parts in your head.
  2. Warm compression vs a known runner; roughly below ~90 PSI warm is a top-end talk.
  3. Ride (or push-start) and feel second engage under load — parking-lot idle lies.
  4. Look for hooked sprockets, soft mounts, and exhaust soot at the flange (gasket leak).
  5. Budget ATF service + carb clean + chain set even on a “runner.”

Use these symptom pages before guessing parts — they route back into this guide:

FAQ (quick)

  • Is a Tomos a scooter? No. A35/A55 are chain-drive pedal mopeds with an automatic two-speed in the cases — not a CVT belt scooter.
  • Premix and gearbox oil? Yes, both. Premix in the tank (typically 50:1 with quality synthetic — confirm for your setup) and Type A/F ATF in the gearbox.
  • A35 vs A55 pipe? Don’t bolt an A35 pipe onto an A55 without checking port angle (A55 often cited at 25° in this guide). Parts are not blindly interchangeable.