Index

Overview

Tuning

Tuning Overview

Lighter Roller Weights

Remove Variator Restrictor

Stiffer Clutch Springs

Move Needle Jet Washer

Increase Fuel Jet Size

Carb De-restriction

Un-Restricted CDI Unit

Un-Restricted Air Inlet

Trouble Shooting

Compression Test

Fuel Enricher Test

Seized Brake Caliper

General Maintenance

Replace Air Filter

Check & Change Oil

Spark Plug Change

Idle Speed Adjust

Change Brake Pads

Adjust Valve Lash

Electrical

Testing the Battery & Charging System

Battery Change

Coil Change

HT Lead Change

Transmission

Remove Starter Motor

Refurb Bendix Gear

Engine

Camshaft Removal

Valve Removal

Replace Valve Guides

Engine Removal



Return to Transport Listings

Models Covered

Lexmoto, Pulse, Sukida, Baotion, Lifan, Direct Bikes, Huatian, JMStar, QT50, LF50QT, YH50QT, BT49qt, 139 QMB, Honda, GY6, Motorbike, Taishan, Jonway, Peugeot V-Clic, QT-4, QT-7, QT-9, qt-11, QT-50 Kymco, Tank, Quinqzi, PGO, Roketa, Strada, Vento, Yamati, QMB139, SunL, SYM, QingQi, Volano Plus Many More Chinese Motorcycles, mopeds and scooters!

Overview of Chinese Import Scooter Tuning Section

Generic 4 Stroke Scooters

Over the past decade the number of imported cheap Chinese 50cc scooters has increased dramatically. These scooters are fairly generic, usually based on a copy of the Honda GY6 139QMB engine and transmission.

The first thing many people think when they first ride one of these imported scooters is, wow, that is SLOW! Out of the crate they usually have very poor acceleration, low top speed and are virtually useless up hills, its probably quicker to get off and walk!

Don't worry, all is not lost. Many people assume that the scooter has been electronically restricted, or the fuel system has been restricted in some way. Whilst that is sometimes the case, this would not account for the terrible acceleration and hill climbing, as electronic restriction should be based on speed, not power.

The list below outlines a number of common reasons for poor performance, some deliberate, some due to poor design or cost cutting. Its important to note that your scooter may have none, some or all (very unlikely) of these issues.



RestrictionCauseEffectSolutiondifficulty RatingSolution Page
Over GearedRoller Weights Too Heavy in VariatorKeeps the scooter in too high a gear, making the engine struggle in acceleration and up hillsFit lighter Roller BearingsMediumRoller Weights
CVT RestrictionBushing Restrictor in the CVTStops the transmission from reaching top gear and hence limits top speedRemove the nylon bush from the VariatorMediumVariator Restriction
Weak Clutch SpringsA weak clutch spring engages the transmission before the engine gets a chance to build up plenty of revsPoor take off from a stand stillFit stiffer clutch springsMedium/HardClutch Springs
Small Fuel JetDoesn't deliver enough fuelLower performance throughout the rev range.Fit a larger Fuel Jet to the CarburetorMediumFuel Jet
Carburetor RestrictionScrew or stud in Vacuum ChamberStops throttle from opening up all the wayRemove Screw or stud and check that throttle slide now opens completelyEasy/MediumCarb De-Restriction
Restricted CDI UnitCDI Unit (computer that controls engine) restricts RPM of the engine Engine cannot rev to max RPM, reduces top speedChange CDI unit, these can be purchased easily onlineEasyCDI Restriction
Carb Needle WasherThe Carburetor Needle washer can be set in a number of different positions, effecting the fuel delivery to the engineRestricts the fuel delivery to the engine, in effect running lean and reducing power.Adjust the washer position on the needle jet in the carbMediumNeedle Washer
Air Intake RestrictionLimiter of some kind in the air intake system to reduce air flow to the engineReduces maximum power as the engine can never get enough airRemove restriction from air inlet ductingEasyAir Intake


What to expect

A de-restricted and properly set up 4 stroke 50cc scooter, chinese or not, should be able to reach about 40mph on the flat with an average sized rider. You won't get much faster than that unless you enter the world of tuning and start fitting performance cams, racing carburetors etc. You will never be able to make a 4 stroke scooter as fast as a 2 stoke scooter. FACT.


Approach to Tuning Your Chinese Scooter

  1. Don't rush out and by Snake Oil type products that promise power gains.
  2. Change one part at a time and note the difference it makes.
  3. Take note of the problem you are experiencing, ie poor hill climbing and acceleration and take appropriate action.
  4. Don't buy a performance air filter, your scooter will probably run worse!




Finally

OK, you have a 50cc 4 stroke scooter that you probably bought off eBay or similar. The piston in your scooter is about the size of a cotton reel so you are never going to be threatening Valentino Rosi!

These pages are not so much about tuning your chinese imported 4 stroke scooter motorcycle, but more about setting it up correctly and removing any factory restrictions, which make the scooter so slow that, frankly, its dangerous.

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