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We recommend a 25:1 or 20:1 gas-to-oil ratio — that's 5 or 6 ounces of 100% synthetic oil per gallon of fuel. We recommend Amsoil Saber Pro or Honda HP2 oil. Always use low-octane gas (87–89 octane) — do NOT use high-octane or race fuel, as this can harm the engine. Once you choose your mix ratio, stick with it. During break-in (typically 1.5–2 gallons of fuel), vary your running speed and avoid full throttle.

Starting points for common Walbro carburetors:

• WT-644 — High: 1½ turns  |  Low: 1½ turns
• WT-603 — High: 1½ turns  |  Low: 1⅝ turns
• WT-488 (big bore) — High: 1⅛ turns  |  Low: 1½ turns
• WT-257 (big bore) — High: 1½ turns  |  Low: 1½ turns
• WT-813 (big bore) — High: 1½ turns  |  Low: 1½ turns

These are starting points only — fine-tune from there based on your engine's response. Not sure which carb you have? Call us at 317-844-4695.

No more than 1 minute. Running longer than that risks overheating and internal engine damage. Also be careful not to over-rev. If you need to run the engine out of the water for longer — for break-in or setup purposes — run a water line from an external source to the engine's water inlet to keep it cool.

Zero Drag Seals install on both sides of the engine crankcase and reduce drag on the crankshaft for improved RPMs and less engine wear.

Tools needed: Flywheel Puller, Zenoah Engine Tool (or same-diameter tubing), Hammer, and a small punch.

Output side (collet side): Slide the zero drag over the crankshaft with the tapered edge toward the seal. Press until it pops flush against the rubber seal face.

Recoil side: Remove recoil, motor plate, flywheel, and the half-moon key from the crankshaft. Press the zero drag in flush. Reinstall the key, flywheel, plate, and recoil.

We offer three header pipe shapes: 90-degree, Wrap-to-Center (WTC), and Vee (V). The right choice depends on your engine compartment layout and tuned pipe configuration. Call us or email if you need help choosing — it's a quick conversation with the right info in hand.

Very important. On V-bottom boats, the balance point should be 27–30% of the total hull length, measured from the transom (back of the boat). For a 50" boat, that's 13.5"–15" from the stern. A nose-heavy boat may never get up on plane and will handle poorly. Adjust your battery, fuel tank, and component placement to hit this range.

Yes — this is normal and expected. It's caused by the torque of the RC boat engine. It can often be corrected or reduced with trim tabs, adjusting the drive angle, or changing your propeller. If the pull is severe, contact us and we can walk you through the adjustment process.

A fail safe is an electronic device that plugs between the throttle servo and the receiver. It monitors voltage and signal frequency. If your battery drops to a level that could cause signal loss, or if the radio link between transmitter and receiver is interrupted, the fail safe automatically closes the throttle to a preset idle position — preventing a runaway boat. We highly recommend one for any boat running at speed on open water.

The general layout places the engine centered and forward, with the fuel tank behind or alongside it, the radio box toward the back, and water cooling lines running from the hull intake to the engine water jacket and back out. For a visual reference, download our engine compartment layout diagram. If you're building from scratch, call us — our team can walk you through it for your specific hull.

A clean water system is critical for keeping your engine at safe operating temperature. Check all lines weekly — blow through them to confirm good flow and look for kinks, debris, or buildup. If you run in salt water, back-flush your entire system with fresh water after every session to prevent salt residue from building up in the water lines and jacket. Neglecting this is one of the most common causes of heat damage to Zenoah engines.

We offer solderless and solder-type drive cable assemblies. Our solderless drive cable assembly uses a round collet-to-square ferrule connection and is what we recommend — it creates a stronger connection than soldering and is easier to work with. View our shaft systems diagram to see the differences visually. Still not sure? Call us and we'll help you pick the right system for your hull.

1. Loosen the two set screws in the shaft ferrule (the tapered cylinder between the transom and shaft strut).
2. Loosen the cable collet compression nut (the 9/16" hex nut on the end of the collet).
3. Slide the propeller shaft toward the rudder until it clears the ferrule.
4. Pull the ferrule down slightly until it clears the strut, then pull the cable straight out the back.
5. Clean the cable, wipe off old grease, spray with penetrating oil, re-grease, and store.

To reinstall, simply reverse the process.

Soft-mounted engine (rubber dampened): approximately ¾" of clearance.
Solid-mounted engine: approximately ½" of clearance.

This gap is essential — it allows the engine to move through vibration without the collet striking and damaging the end of the stuffing tube.

We recommend going solderless if possible (see above). But if you need to solder, here's what we use:

Solder: Stay-Brite Silver Solder with its own flux. Heat source: Propane torch with Mapp gas (burns hotter).

Process: Lightly sand the cable end, clean with acetone, apply flux, and slide the ferrule over. Clamp the assembly vertically in a vise with the cable hanging down. Drop 3 small pieces of solder (approx. 1/8") into the ferrule. Heat the outside of the ferrule — working around the perimeter — until the solder flows. Pull the heat away immediately. Never apply heat directly to the cable — this removes the temper and causes failure.

Not at all — this is intentional. The lower-right hole and upper-right threaded hole on the Z-Plate have the anodized coating machined away. This is done for grounding purposes: the grey ignition coil must make an electrical ground all the way through to the main crankcase, and the exposed metal areas ensure that connection is made. Your plate is not damaged.

1. Remove all fuel. Pump or siphon the tank, then fire the engine and let it idle until it runs out of fuel — this clears the carb and lines.
2. Fog the engine. Remove the spark plug and pour about 1 oz. of lightweight cylinder lube (e.g., Marvel Mystery Oil) into the plug hole. Pull the starter cord 7–10 times slowly to work the oil through the rings and bearings. Reinstall the plug.
3. Service the drive cable. Remove it, clean off old grease and any water or rust, lubricate, and reinstall.
4. Discharge batteries partially. Don't store rechargeable batteries fully charged or fully dead — partial discharge prevents memory problems.
5. Protect metal parts. Spray exposed metal components with WD-40 or similar penetrating oil and wipe down to remove moisture and prevent corrosion.

Yes. Download the RTR Boat Owner's Manual (PDF) from the BONZI Sports website. If you have questions about your specific model that aren't covered in the manual, call us at 317-844-4695.