There is no universal best big bore kit for a 50cc scooter: the right choice depends on the exact engine, not just the scooter’s model name or advertised displacement. First confirm whether the engine is two-stroke or four-stroke, its layout and cooling, and the cylinder, case and wrist-pin dimensions. Then check what tuning parts and road-use restrictions apply.
How to choose a big bore kit that fits
Use this checklist before comparing brands or prices:
- Identify the engine. Confirm the exact engine family and configuration, including two-stroke versus four-stroke and air versus liquid cooling. Model names alone do not establish compatibility.
- Verify dimensions. Match the bore, wrist-pin diameter, sleeve and crankcase clearance to your engine. A kit intended for one engine family may not fit a visually similar clone.
- Check kit contents. Compare the included cylinder, piston, rings, pin, circlips, gaskets and any supporting parts. Confirm separately whether a wrist-pin bearing, exhaust gasket or other required part is included.
- Plan the supporting tune. Account for carburetor or fuel-system changes and, where the package calls for them, exhaust and transmission tuning. Do not assume the cylinder alone is a complete performance setup.
- Confirm intended use and local rules. Read the product’s emissions and road-use restrictions, then check licensing, registration, insurance and emissions requirements where the scooter will be operated.
Examples of kits—and what their fitment means
The following products illustrate why the choice must be engine-specific. They are not a head-to-head test, and neither is a universal recommendation.
Naraku 70cc kit for horizontal Minarelli two-strokes
Scooterworks USA lists the Naraku 70cc Big Bore Cylinder Kit for air-cooled, horizontally mounted Minarelli two-stroke engines. The listing gives a 47 mm bore, a 10 mm wrist pin and a 50.5 mm sleeve outer diameter; it says the kit can use the stock crankshaft. Included parts are the cylinder, piston, rings, pin, circlips and head, base and exhaust gaskets. The wrist-pin bearing is not included.
#1 Best Overall
- Use Large Valve Heads to Get More Power for Your GY6 139QMB 139QMA 147QMD Scooter ATV Go Kart Engine!!
- This Big Bore Rebuild Kit Comes with 18.5/20.5mm Large Valve Cylinder Head Assy (Stock is 16/18.5mm).
- Compatible with 69mm Long Valve Style Heads. If your Original Head Has 64mm Valves, Please Must Change Your Rocker Arms with The Ones in Our Kit.
- Glixal Piston Rings: DLC Wear Resistant Coating. This Coating will Also Reduce the Friction Coefficient to Protect the Cylinder Sleeve.
- Please Note: The Engine Side Cover Gasket is for a Short Case Version (8 Bolt).
The listing names Yamaha Jog and Zuma among its application examples but tells buyers to verify engine configuration and pin size, including on Chinese clone engines. It also warns that some cases may need light filing or machining to clear the sleeve. The seller identifies this product as off-road use only. These details make it a candidate only when the engine and dimensions match—not simply because a scooter is labeled “50cc.”
Stage 2 package for Genuine Buddy and RoughHouse 50
Scooterworks USA’s Stage 2 Performance Kit for Genuine Buddy 50 and RoughHouse 50 is a model-oriented package that the listing also identifies for the Genuine Black Cat 50 and Rattler 50. It contains a Malossi 70cc iron cylinder, an NCY expansion pipe, a contra spring, Prima roller weights and Keihin jets. The exhaust gasket is sold separately. The listing says other Minarelli-style engines require compatibility checks.
Rank #2
- This big cylinder kit will upgrade your gy6 50cc 60cc 80cc to 100cc, without EGR, to get more RPM,more power, faster maximum speed.
- 64mm valve length version
- Easy Installation
- Upgrade engine parts included cylinder body kits, cylinder head kits, camshaft, camshaft seat kits, gaskets kits, oil pump and gear, clutch spring sets, copper roller sets, 6pins racing AC CDI, ignition coil and racing 3-electrode spark plug
- Upgrades parts kits for most of 50cc scooter
This package is explicitly intended for off-road and closed-course competition use only. The seller says it is not EPA or CARB compliant and is not legal for use in California on pollution-controlled vehicles. Those are the listing’s stated restrictions; they should not be generalized into a legal conclusion for every product or jurisdiction.
Four-stroke applications are a separate path
Two-stroke and four-stroke kits are not interchangeable. KITACO publishes separate application information for two-stroke scooter kits and four-stroke scooter kits. Its four-stroke information describes a light kit that can be used with the stock cylinder head, but fitment remains application-specific. Match the actual engine and application rather than carrying over a two-stroke kit’s dimensions or tuning advice.
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteRank #3
- Specification: Upgrade Cylinder size: 50mm, Piston: 50mm,Valve:69mm, Clutch Spring:1500RPM,
- Advantage: A9 crankshaft, High Performance CDI, Ignition coil,Spark Plug, 6.5g Copper Roller.
- Fitment: kit fits for most 49cc 50cc Chinese scooters mopeds & ATVs equipped with 139QMB 139QMA 4 stroke engine. Such as Taotao, Jonway, Jmstar, Roketa, Sunl, Sunny, Vitacci, Icebear, Lance, Xpro, Tank, Peace, Dongfang, Kazuma, JCL, BMS, Baja, Baccio, Eagle, Urban, Panterra.
- Compatibility: Taotao 49cc 50cc scooter moped(VIP Future Champion 50/ ATM50-01/ Pony 50/ Thunder 50/ CY50-A, CY50-B, CY50-T3/ New Speed 50/ EVO 50/ Blade 50/ Classic 50/ Euro 50cc), Baja SC50, Jonway 50cc, Vitacci 50cc, Roketa 50cc, Jmstar 50cc, Wol* 50cc scooter(RX50/ Islander/ V50/ Rugby), Ice Bear 50cc, Lance 50cc , Wildfir* 50cc, X-Pro 50cc, Sunl 50cc, Sunny 50cc, Peace Sports 50cc, Zongshen 50cc, Tank 50cc, Panterra 50cc, Piaggio 50cc.
- Package Included: 50mm cylinder body kits, cylinder head kits, A9 camshaft, camshaft seat kits, gaskets kits, oil pump and gear, spring sets, copper roller sets, 6pins racing AC CDI, ignition coil and racing 3-electrode spark plug
What else may need to change
Increasing displacement changes the engine’s air and fuel requirements. KITACO says its two-stroke applications require either a larger carburetor or adjustment of the stock carburetor. The Naraku listing recommends a main jet typically 10–15% larger for a 50-to-70cc conversion. That percentage is seller guidance, not a guaranteed setting for every engine, carburetor or altitude.
A package can also call for other parts or tuning. The Buddy/RoughHouse example bundles an exhaust, contra spring, roller weights and jets with its cylinder; the Naraku listing flags possible case-mouth clearance work and excludes the wrist-pin bearing. Follow the instructions for the exact kit. If you cannot safely measure clearances, machine a case or tune the fuel system, use a qualified mechanic. The available product information does not establish a universal carburetor, jet, variator, crankshaft or break-in setup.
Rank #4
- 1.Inner Diameter of Cylinder: 47mm
- 2.Outer Diameter of Piston Pin: 13mm
- 3.High Quality Durable Piston Rings
- 4.Include Cylinder,Piston,Piston Ring,Piston Pin,Piston Pin Clip,Valve Oil Seal,Gaskets,Tensioner Gasket,Exhaust Gasket,Intake&Exhaust Studs,Exhaust Nut
- 5. High Performance Upgrade 47mm Cylinder Rebuild Kit for GY6 49cc 50cc 60cc 80cc engine
Performance gains: what is and is not established
A larger cylinder is intended to increase displacement, but the cited product information does not establish a measured horsepower, torque or top-speed gain for a specified scooter-and-kit combination. KITACO describes increased power and torque for its listed four-stroke kit but provides no numerical test result in the cited information. Do not treat the 70cc displacement, 47 mm bore or suggested jet increase as a measured performance result, or assume a particular speed increase.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check road legality before buying or installing
Restrictions depend on the product and where the scooter is registered and operated. For the Stage 2 Buddy/RoughHouse package, Scooterworks USA states: “For off-road and closed-course competition use only. Not EPA or CARB compliant. Not legal for use in California on pollution-controlled vehicles. Check local laws before installing.”
Free tools Windows power users keep installed
One-click scans. No signup required.
Best Value
- This big cylinder kit will upgrade your gy6 50cc 60cc 80cc to 100cc, without EGR, to get more RPM,more power, faster maximum speed.
- 69mm valve length version
- Simple Installation
- With cylinder body kits, cylinder head kits, camshaft, camshaft seat kits, gaskets kits, oil pump and gear, spring sets, copper roller sets, 6pins racing AC CDI, ignition coil and racing 3-electrode spark plug
- Upgrades parts kits for most of 50cc scooter
KITACO’s road-use guidance discusses Japanese procedures for a 50cc-engine big bore, including possible modification notification, licensing and registration requirements. That guidance is specific to its Japanese context and does not determine legality elsewhere. Before modifying a road vehicle, check the rules that apply to your location and vehicle, including licensing, registration, emissions and insurance.
Which option should you choose?
- If your scooter has a verified air-cooled horizontal Minarelli two-stroke: the Naraku listing is a possible cylinder-kit path if its bore, 10 mm pin and case dimensions match your engine, and its off-road-only limitation suits your intended use.
- If you have a compatible Genuine Buddy, RoughHouse, Black Cat or Rattler: the Stage 2 package offers a cylinder with supporting tuning parts, but its stated off-road, emissions and California restrictions may rule it out for road use.
- If your engine is a four-stroke or a different layout: look only at an application listed for that engine. KITACO’s separate four-stroke information illustrates that a four-stroke kit is a distinct fitment path, not a substitute for a two-stroke kit.
If you cannot confirm the exact engine and dimensions, do not order based on nominal 50cc displacement alone. A fitment check against the scooter’s engine code and the kit manufacturer’s specifications is the most useful next step.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
