Walbro WT-1107 Carburettor: Specs, Fitment and Tuning for Large-Scale RC
The Walbro WT-1107 is a diaphragm carburettor used on 2-stroke engines in large-scale RC. It’s standard on the Zenoah G320 (32 cc) and is a popular upgrade for Zenoah and CY-type engines in 1/5 cars like the HPI Baja and in gas RC boats. It has a 15.88 mm bore, a 13.5 mm venturi (larger than many stock carbs) and separate high- and low-speed needles, so it flows more fuel and air for extra power when tuned correctly.
By Kyle HilsonUpdated: October 20263 min read
Specifications
| Item | Value |
|---|---|
| Type | Diaphragm carburettor |
| Bore | 15.88 mm |
| Venturi | 13.5 mm |
| Adjustments | High-speed (H) and low-speed (L) needles, idle screw |
| Stock on | Zenoah G320 (32 cc) |
| Common use | Upgrades on Zenoah/CY 23–32 cc engines in 1/5 cars and boats |
From dealer listings, checked October 2026. Fitment to smaller engines may need an adapter or intake changes.
Why upgrade to the WT-1107
Many 1/5 cars come with smaller carburettors that limit airflow. A larger venturi lets a modified engine (ported, with a tuned pipe) breathe and make more power. On a stock engine the gain is smaller, and an oversized carb can make low-speed running less crisp. The WT-1107 suits engines that have been upgraded or are large enough to use its flow, which is why it’s a favourite in gas boat racing and big-bore car builds.
Fitting it
- Check that the intake manifold and air filter adapter match the carb.
- Use a new gasket and reed or insulator block as required.
- Connect the fuel line to the inlet and the pulse line if your engine uses one.
- Set up the throttle linkage so the servo opens fully and closes to idle without binding.
- Check for air leaks: leaks cause lean running and engine damage.
Tuning basics
Commonly quoted starting points are both mixture needles at about 1¼–2 turns open from lightly seated, with the idle screw about 2 turns in, but follow the instructions for your engine. The low needle (closest to the engine) sets idle and acceleration; the high needle (closest to the intake/choke) sets top-end mixture. Tune in small steps of 1/8 turn: lean (clockwise) for more revs, rich (anticlockwise) for more cooling. If the engine screams then bogs, it’s too lean; if it smokes heavily and won’t rev, it’s too rich. Always leave the high end slightly rich to protect the engine.
Common problems
- Hard starting: check the fuel pump diaphragm and that fuel reaches the carb.
- Bogging on acceleration: low needle too lean or too rich.
- Hanging high idle: air leak or throttle linkage not closing.
- Flooding: inlet needle or metering diaphragm issue; rebuild kit.
- Loss of power after storage: old fuel stiffened the diaphragms.
Care
Run the carb dry or use stabilised fuel for long storage, keep the air filter clean and oiled, and replace diaphragms and gaskets with a rebuild kit when performance drops. Zenoah engines it fits are covered in Zenoah boat engines, and fast 1/5 cars in the fastest 1/5 scale gas RC cars.
Genuine vs copies
Cheap copies of Walbro carbs are common. They may work, but metering quality varies and tuning can be inconsistent. Genuine Walbro carbs from known dealers are more predictable, which matters on expensive engines.
FAQ
What engines use the Walbro WT-1107?
It’s stock on the Zenoah G320 and fitted to many Zenoah/CY engines.
Does it fit an HPI Baja?
Yes, with the right intake parts.
What are the starting needle settings?
About 1¼–2 turns open on both needles; check your engine’s guide.
Will it add power?
Mostly on modified engines.
More on this topic: the complete RC Cars guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
