Zenoah Boat Engines: G260PUM, G290PUM and G320PUM Compared
Zenoah’s water-cooled “PUM” engines are the classic choice for RC gas boats. The G260PUM is a 25.4 cc two-stroke rated at 3.25+ hp at 12,500 rpm with a Walbro WT-257 carburettor; the G290PUM is 28.5 cc and about 3.5 hp at 13,000 rpm, weighing about 1.6 kg; and the G320PUM is 31.8 cc, rated at 4.36 PS at 14,000 rpm and around 1.9 kg, often fitted with the Walbro WT-1107. They power monos, riggers, hydros and cats in many gas racing classes, and a whole industry of performance parts has grown around them.
By Kyle HilsonUpdated: October 20263 min read
The engines compared
| Engine | Displacement | Power | Notes |
|---|---|---|---|
| G260PUM | 25.4 cc (34 × 28 mm) | 3.25+ hp @ 12,500 rpm | Walbro WT-257; popular racing base |
| G290PUM | 28.5 cc (36 × 28 mm) | 3.5 hp @ 13,000 rpm | About 1.6 kg |
| G320PUM | 31.8 cc (38 × 28 mm) | 4.36 PS @ 14,000 rpm | About 1.93 kg; often with WT-1107 |
From dealer specifications, checked October 2026.
Why Zenoah dominates
Zenoah engines are reliable, easy to start and widely supported. Water-cooled heads keep them at stable temperatures in a closed hull, and their size suits the 23–35 cc classes used in gas boat racing. Tuners offer ported cylinders, tuned pipes, bigger carburettors and ignition upgrades, so the same engine can serve a beginner sport boat or a modified racer. Spare parts are stocked by many boat dealers.
Choosing an engine
- G260: lighter, for 26 cc classes and smaller hulls.
- G290: a middle ground with more torque.
- G320: the most power, for larger boats and open classes up to about 35 cc.
Check your racing class rules and your hull’s recommended engine size before buying. Gas power in general is compared with electric in RC boat motors.
Installation basics
- Mount the engine on solid engine mounts aligned with the flex shaft.
- Connect the clutch and collet to the flex shaft with correct engagement.
- Route cooling water from a pickup through the head and out of the hull.
- Fit the tuned pipe or muffler with a water-cooled header.
- Connect throttle and choke linkages to servos, and fit a kill switch.
- Seal the radio box well away from the engine.
Carburettors and tuning
The stock carbs work well, but many racers upgrade to a larger carb such as the Walbro WT-1107 on modified engines. Tune high and low needles in small steps, run slightly rich for safety, and check plug colour and cooling water temperature.
Care
- Use fresh fuel with the oil ratio the engine maker specifies.
- Check cooling flow every run.
- Clean air filters and check plugs regularly.
- Run the engine dry or use stabilised fuel before storage.
- Replace fuel lines and pump diaphragms when they harden.
Break-in
New engines should be run gently and slightly rich for the first tanks, avoiding long full-throttle runs. Follow the maker’s break-in advice; a carefully broken-in engine lasts longer and makes more power later.
Safety
Gas boats are fast and heavy. Run only where permitted, keep clear of swimmers and wildlife, store fuel safely and always test the kill switch before launching.
Keep a log of fuel mix, needle settings and props so you can return to a known good setup after changes.
FAQ
Which Zenoah engine is best for an RC boat?
It depends on class and hull: G260 for 26 cc, G320 for more power.
Are Zenoah boat engines water-cooled?
Yes, the PUM marine versions are.
What fuel do they use?
Petrol mixed with two-stroke oil.
Can I upgrade the carb?
Yes, many use the Walbro WT-1107 on modified engines.
More on this topic: the complete RC Boats 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
