The Tomos A35 (1991–2006) is a reed-valve 49cc engine with an automatic two-speed transmission inside the cases — chain to the rear wheel, not a belt variator. Stock specs: 38×43 mm bore/stroke, 9.1:1 compression, Dellorto SHA 14/12 with #53 main jet, NGK BR6HS on CDI bikes. Do not confuse with the later A55 (piston-port, PHVA carb, 25° exhaust angle).
Build comparison
| Tier | Goal | Key parts | Realistic top speed | Budget |
|---|---|---|---|---|
| Mild | Reliable runner | SHA clean, stock #53 baseline, ATF gearbox, fresh reeds | 30–35 mph | $50–$175 |
| Mid | 70cc commuter | 70cc kit, A35-fit pipe, jet up, two-speed clutch tune | 40–45 mph | $400–$700 |
| Wild | Race reed | Ported 70cc+, performance reeds, pipe, clutch pucks, ignition | 48–52+ mph | $800–$1,400+ |
Know the platform
- Reed block — Two-petal flat reed on stock A35; leaky reeds cause oily cases and weak low-end.
- Gearbox oil — Type A or Type F ATF, separate from 50:1 premix in the tank.
- Ignition — 1.5 ± 0.2 mm BTDC advance; points gap 0.35–0.45 mm on pre-CDI (1991–1994).
- Exhaust angle — A35 pipes do not bolt to A55 without bending (25° port on A55).
Build 1 — Mild
- Ultrasonic or manual SHA teardown; new intake O-ring; verify choke cable.
- Stock jet baseline #53 — plug-chop after any air filter change.
- Drain and refill gearbox with correct ATF; adjust chain ~10 mm slack.
- Inspect reed petals and cage gaskets; replace if oil-soaked.
Design pipe for this tier — broad peak for stock reed timing (22 mm exhaust height example). Pipe + jetting after derestrict.
Build 2 — Mid
- 70cc kit with port match to A35 case transfers.
- Pipe designed for A35 reed timing — not a random Puch pipe.
- Two-speed clutch: worn pucks cause hang-in-first; shim and spring condition matter as much as jetting.
- Step main jet gradually; SHA numbers do not match Bing.
Design pipe for this tier — balanced peak, Alukit pipe RPM 9500–9700 documented on Moped Army. Measure kit port duration.
Build 3 — Wild
- Ported cylinder with measured durations; reeds upgraded to performance petals.
- Larger SHA or PHBG carb with matched intake; rich break-in premix.
- Clutch and second-gear engagement tuned for high-RPM pulls — slipping in second wastes top speed.
Design pipe for this tier — sharp peak, Airsal kit ~9800 RPM documented. Ported reed — tune second-gear clutch to match.