Free printableTroubleshootingTSP-TS-05FLAGSHIP
GY6 poor acceleration and no top speed
It runs, but it will not pull. The first question separates a transmission fault from an engine fault, and almost nobody asks it.
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TSP-TS-05 · version v1.0 · September 2026. Opens in your browser's PDF viewer, where you can print directly.
The problem it solves
“It has no power” is the vaguest fault an owner can report and the one most likely to be answered with a parts list. It covers a slipping belt, a worn engine, a lean mixture, a restricted air filter and a soft rear tyre — problems with nothing in common except the symptom.
There is one question that splits this fault in half, and it costs nothing to answer: when you open the throttle and it will not pull, does the engine rev higher than it should while the speed stays down, or does it stay flat and low?
Revs rising without speed is slip. The engine is making power and the transmission is not delivering it, which points at the belt, the clutch or the pulley faces. Revs staying low and flat is the opposite: the transmission is holding but the engine has nothing to give, which points at compression, mixture or a restriction.
Everything after that first branch follows from it, and the two halves share almost no components. Asking it first is the difference between an afternoon and a month.
The mistakes this sheet exists to prevent
- Fitting a new belt for a fault where the revs never rose — which means it was never slipping.
- Fitting lighter rollers to "get more acceleration" on an engine that has low compression, which makes it worse.
- Ignoring tyre pressure, which the most consistent source in this niche calls out as having a major effect on speed.
- Diagnosing the mixture from the plug alone. One signal can mislead; the table on this sheet gives four.
- Comparing top speed against what a forum says the model should do, rather than against what this machine used to do.
Who it is for
- Anyone whose machine has gradually got slower
- Owners who lose speed uphill but are fine on the flat
- Anyone about to buy CVT parts to fix a power problem
What is on it
- The revs-versus-speed split that halves the problem in one question
- Separate branches for slip and for engine weakness
- The rich-versus-lean symptom table
- Cranking compression benchmarks, with their single source named
How to use it
- 01Answer the first question honestly, on a ride, before opening anything.
- 02Check tyre pressures before blaming the engine. It is free and it is a documented cause.
- 03Follow only the branch your first answer sends you down.
- 04Record the compression figure so the next test has something to compare against.
Use it with the registry
Other sheets you may want
- GY6 CVT slipping, juddering and squealingThree different noises from the same case, and they mean different things. What to look at with the cover off, in order.
- GY6 starts then dies, or will not idleIt fires, runs for a few seconds and stops. Or it only idles with the throttle cracked open. Four causes account for most of it.
- CVT service record for a GY6 or Chinese scooterThe transmission is the highest-wear system on a scooter and the least documented. One sheet for everything that goes in it, with the measurements taken each time.
Free to print, copy, and share — including in forums, clubs and workshops. If you find a mistake on this sheet, tell us and it gets corrected. Quote TSP-TS-05 and the version so we know exactly which sheet you mean. All printables.