The AV7 is Motobécane's long-running piston-port 49cc engine. On US imports the 50V model pairs AV7 with a variator — not a single-speed Puch. Base 50 models used a dimoby single-speed transmission instead. Identify your frame (50 vs 50V) before ordering variator parts. Gurtner and Encarwi carbs use their own jet numbering.
Build comparison
| Tier | Goal | Key parts | Realistic top speed | Budget |
|---|---|---|---|---|
| Mild | Free Moby | Clean tank/petcock, variator service, derestrict exhaust, Gurtner tune | 25–32 mph | $50–$200 |
| Mid | ParmaKit daily | AV7 cast kit, matched pipe, roller weights, port match | 38–43 mph | $400–$750 |
| Wild | Ported race | Raised exhaust port, performance variator plate, aggressive port map | 45–50+ mph | $850–$1,500+ |
Know the platform
- 50V variator — 36 mm left-hand nut holds the back plate; grease balls on service. Performance plates change ramp profile.
- Speed rating — Factory 20 / 25 / 30 mph classes tied to cylinder porting (CS stamps on some jugs). Measure your port map before assuming you have a "fast" cylinder.
- Exhaust — Stock crushed pipe caps RPM; open exhaust always pairs with jetting.
- Encarwi float — Float-pin height (~12–12.5 mm) tunes part-throttle; main jet tunes WOT — adjust together.
Build 1 — Mild
- Fuel system: rust-free tank, brass pickup tube, inline filter, rebuilt petcock.
- Variator disassembly, clean ramps, inspect balls and starter clutch pads.
- Exhaust derestriction and carb clean — jet only after airflow is honest.
Design pipe for this tier — broad peak, stock 130° exhaust documented on Moped Army. Derestrict before sizing a performance pipe.
Build 2 — Mid
- AV7 ParmaKit or equivalent with port alignment to case.
- Performance exhaust for Moby angle — bracket work common when adapting foreign pipes.
- Roller weight and spring combo so the variator lets the kit breathe past midrange.
- Document port heights against the port database for your CS-rated cylinder.
Design pipe for this tier — balanced peak, mild port target 145° per Motobecane_porting_the_right_way. Pairs with SHA 15–16 and ParmaKit.
Build 3 — Wild
- Porting with measured transfers and exhaust duration — compare to documented fast-cylinder maps.
- Performance variator plate; minimum roller weight with stiff contra spring.
- Matched pipe and carb bore; plan on richer premix and frequent plug checks.
Design pipe for this tier — sharp peak, 169–175° piped band. Compare your cuts to the Motobecane port database map.