| Engine will not start | - Flat or dead starter battery
- Stale fuel or blocked carburettor
- Fouled spark plug
- No spark: coil, CDI or stator
- Kill switch, stand switch or immobiliser
- Fuel tap, pump or line fault
- Blocked exhaust
- Low compression
- Seized engine
| - Does the starter turn the engine, and does the kickstart meet firm resistance?
- Kill switch, side-stand switch and brake-lever switch: many scooters will not crank unless a brake is held.
- How old is the fuel? Stale fuel smells sour and varnishes the carburettor.
- Look at the spark plug: wet, black and oily, or clean.
- Outdoors only, and away from fuel vapour if you check for a spark.
| - A video of the attempted start with sound.
- When it last ran and what changed since.
- Receipts for anything already replaced.
| Basic to Advanced, depending on the cause Diagnosis time: 1–3 hours Safety-relevant | A battery or plug is a small purchase. Carburettor cleaning costs time rather than parts. Ignition components, a top-end rebuild or a seized engine move this into workshop money — and you may not know which you have until you are some hours in. | - Engine will not turn at all and the price assumes it is a small fault.
- Water or milky oil in the engine.
- Seller has “tried everything” and cannot say what.
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| Throttle sticks, is stiff or does not snap back | - Frayed, kinked or dry throttle cable
- Throttle cable routed wrongly
- Sticking twist grip or carburettor slide
| - Engine off: open the throttle fully and let go. It must snap shut, at full left and full right lock as well as straight ahead.
- Look along the cable for kinks, fraying at the ends and tight bends.
- Check the twist grip turns freely on the bar and is not fouled by the bar end or grip.
| - Whether the cable has been replaced, and with what part number.
- Two-strokes: whether the oil-pump cable was adjusted at the same time.
| Intermediate to Advanced, depending on the cause Diagnosis time: Under an hour Safety-critical | The cable itself is inexpensive. The job is not trivial: panels come off, the cable must follow the original routing, the correct variant for that frame and carburettor is required, and free play is set to the maker’s figure. On two-strokes with a split cable, the oil-pump side must stay in step. | - You cannot identify the correct cable for the variant.
- The throttle still hangs open after the cable is ruled out — the fault is in the grip or carburettor.
- You are not able to do, or pay for, a proper return-to-idle check afterwards.
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| Lights, indicators or charging not working | - Blown bulb or fuse
- Flat or dead starter battery
- Regulator/rectifier or stator fault
- Corroded or chafed wiring
| - Battery voltage at rest and, if it runs, with the engine running.
- Fuses, bulbs and earth connections.
- Look for green corrosion in connectors and chafed wiring around the headstock.
| - What works and what does not.
- Whether the battery keeps going flat.
- Any non-standard wiring, alarm or accessory.
| Basic to Advanced, depending on the cause Diagnosis time: 1–3 hours Safety-relevant | Bulbs and fuses are trivial. A regulator or stator is a moderate parts cost with some dismantling. Chasing an intermittent wiring fault can take longer than any other job on the machine. | - Burnt connectors or melted loom.
- Amateur rewiring you cannot follow.
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| Engine revs but drive slips or is absent | - Worn CVT belt or rollers
- Worn clutch
| - On the stand, does the rear wheel turn when revs rise?
- Listen for rattles from the variator cover.
- Ask when the belt and rollers were last changed.
| - Mileage since the last belt.
- Whether the variator has been modified.
| Intermediate to Advanced, depending on the cause Diagnosis time: 1–3 hours Safety-relevant | Belts and rollers are service parts, but the variator and clutch nuts need the right holding tool and torque. A worn clutch or damaged pulley faces add cost. | - Tuning parts of unknown origin fitted.
- Oil inside the transmission case.
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| Old tyres, seized or weak brakes | - Tyres perished with age
- Seized brakes
- Worn brake pads
| - Read the four-digit date code on the tyres and look for cracks between the tread blocks.
- Push the machine: do the brakes drag or stay on?
- Lever feel, fluid level and colour, pad thickness.
| - Tyre age.
- When brake fluid was last changed.
| Intermediate to Professional, depending on the cause Diagnosis time: Under an hour Safety-critical | Two tyres fitted and balanced, pads, fluid and possibly a caliper rebuild add up fast on a low-value machine. Count them all before you offer. | - Seized caliper plus perished tyres on a machine with thin resale value.
- Any damage to a wheel rim.
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| Papers missing or identifiers do not match | - Ownership or registration documents missing
- Frame or VIN number does not match the papers
- Derestricted beyond its legal class
| - Compare the frame number on the machine with the document, digit by digit.
- Look for re-stamped, ground or welded areas around the number.
- Check what your country requires for this class before you travel.
| - Photo of document and frame number together.
- Seller’s ID matching the document where that is normal in your country.
- A written sales agreement.
| Professional Diagnosis time: Under an hour Safety-critical | Replacing lost documents can be slow, costly or impossible depending on the country — and is the owner’s job, not yours. | - Number missing, altered or not matching.
- No document and a story instead.
- Derestricted and sold as a standard moped.
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