WILLIAMS 400 SportJet
(Rotax 1503 Engine)
Technical Guide, Maintenance and Spare Parts
This generation of the Williams SportJet 400 is equipped with a BRP Rotax 1503 engine, a 1,494 cm³ four-stroke three-cylinder engine. In the original Williams documentation provided for this item, this version is rated at 125 HP with a top speed of approximately 71 km/h (44 mph).
With its 4.09-meter length, 5-person capacity, and 75-liter fuel tank, the SportJet 400 is designed for use as both a yacht tender and for water sports.
At Rotax Tender Parts, we offer maintenance and replacement parts for Rotax engines and Williams tenders: filters, spark plugs, sensors, relays, fuel systems, seals, and propulsion block components. Accessories, calibrations, and certain part numbers vary depending on the engine and model year. Before placing any order, check the OEM part number, year, and engine serial number; simply stating "Rotax 1503" is not sufficient to guarantee compatibility.
Find Parts for Your WILLIAMS SportJet 400 – Rotax 1503
- Engine parts
- Fuel system
- Ignition
- Sensors
- Electrical parts
- Cooling
- Oil and filters
- Seals and gaskets
- Turbine block parts
- Other
Technical Specifications of the Williams SportJet 400 – Rotax 1503
- Overall length: 4.09 m.
- Width: 2.01 m.
- Height: 1.40 m.
- Draft at full load: 0.42 m.
- Dry weight: 520 kg.
- Engine: BRP Rotax 4-TEC 1503, three-cylinder, four-stroke.
- Displacement: 1,494 cm³.
- Manufacturer's rated power: 125 HP.
- Propulsion: jet.
- Top speed: approximately 71 km/h (44 mph).
- Capacity: 5 people.
- Fuel tank: 75 liters.
- Maximum load: 675 kg.
- Tube compartments: 5.
- CE category: C.
- Fuel: unleaded gasoline.
Specifications may vary depending on the year of manufacture and tender configuration. It is recommended to check the engine serial number before ordering any parts.
Maintenance Schedule – Williams SportJet 400
The Williams SportJet 400 maintenance program distinguishes between checks to be performed at each use, after the break-in period, at regular intervals, and at the end of the season.
For all operations specific to the Rotax 1503 engine, the recommendations in the Rotax engine manual must also be followed.
| Item | At each use | 10-hour break-in | Every 60 hours | End of season |
|---|---|---|---|---|
| Turbine block / propulsion block | Inspect | ✓ | ✓ | — |
| Propulsion block anodes | Inspect / replace if necessary | ✓ | ✓ | ✓ |
| Carbon ring and shaft bellows | Dealer check every 100 hours or before the season | — | — | — |
| Bilge | Inspect / clean | ✓ | — | ✓ |
| Electrical connections | Inspect / clean / lubricate | ✓ | — | ✓ |
| Fuel system | Inspect | ✓ | — | ✓ |
| Ignition / battery disconnect | Inspect / clean / lubricate | ✓ | ✓ | ✓ |
| Reverse cable | Inspect / clean / lubricate | ✓ | ✓ | ✓ |
| Steering cable | Inspect / clean / lubricate | ✓ | ✓ | ✓ |
Routine Maintenance Recommended by Williams
In addition to the periodic schedule, Williams recommends, in particular:
- regularly washing the tender with fresh water to remove salt deposits;
- checking the engine oil level;
- checking the coolant level;
- flushing the open cooling system;
- greasing the control cables on both the console and propulsion block sides;
- checking the bilge for water, oil, or fuel;
- regularly checking the condition of the anodes;
- regularly checking the tube pressure.
After Use in Salt Water
After use at sea, rinsing is particularly important. In particular, you should:
- rinse the tender with fresh water;
- perform the engine flushing procedure;
- rinse the turbine block and propulsion area;
- check the intake screen;
- check the condition of the anodes;
- inspect the engine compartment;
- monitor electrical connections and check for any signs of corrosion.
Intensive use or use in a tropical environment may require more frequent maintenance intervals. Follow the procedure in your manual; also consult our engine flushing guide.
Common Parts for the WILLIAMS SportJet 400 – Rotax 1503
This selection is based on the Williams SportJet 400, 460, and 520 range equipped with the Rotax 1503 engine. OEM part numbers identify the replaced parts; they do not automatically refer to genuine parts. Click on a "Buy" thumbnail to add one product to the cart and access the cart. When the batch or version requires a choice, the "Choose the version" thumbnail opens the product page. The names and part numbers retain their links to the product pages.
iNR components apply only to tenders equipped with this option; the engine overhaul parts in the second table require specific validation for the 125 HP engine.
| Buy | Part | OEM Part Number | Function |
|---|---|---|---|
 |
Compatible NGK DCPR8E spark plug | 5297630 ; NGK DCPR8E / 4339 | Ignition; listing citing the SportJet 400. Confirm the engine manual specification. |
 |
Ignition coil | 420666142 | Spark production; declared 400 / 460 / 520 application. |
 |
35 A / 12 V relay, single unit | 278002822 / 278003828 ; Williams 02-0860 | Switches electrical circuits. |
 |
35 A / 12 V relay, pack of 5 | 278002822 / 278003828 ; Williams 02-0860 | Electrical switching; workshop packaging. |
 |
Starter solenoid relay | 278000513 / 278002347 / 278001802 / 278001766 ; Williams 02-1108 | Switches starter power supply. |
 |
12 V power relay | 278003012 ; Williams 06-0521 | Electrical switching; check the installed circuit and relay. |
 |
Voltage regulator / rectifier | 710001103 / 0460375 ; Williams 02-1013 | Voltage regulation and charging; compare reference and connectors. |
 |
Fuel pump strainer, pack of 2 | 270600113 | Fuel pre-filtration. |
 |
Crankshaft position sensor | 420966575 / 420966570 | Crankshaft position reading. |
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Camshaft position sensor | 420664045 ; Williams 02-1089 | Engine management synchronization. |
 |
Coolant Temperature Sensor | 278002895 / 278001016 ; Williams 02-1065 | Temperature monitoring; reference and location to be verified. |
 |
Oil Pressure Sensor | 420856533 / 55233423 | Pressure monitoring; check the actual pressure before concluding that the sensor has failed. |
 |
Magneto Housing / PTO Cover Gasket | 420931130 | Cover sealing; stated SportJet application, cover to be identified. |
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iNR Connector Housing, per unit | 278002880 | Wiring repair, only with the iNR option and corresponding housing. |
 |
Rotax 1503 / 1630 Oil Filter | 420956744 | Oil filtration; stated SportJet 400 application. |
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Oil Filter, other offer | 420441373 / 420956744 | Other offer for installation using filter 420956744. |
 |
Oil Filter O-Rings, pack of 10 kits of 3 | For filter 420956744 | Filter assembly sealing; 420956744 designates the associated filter, not the individual O-rings. |
 |
Silent Block / Motor Mount | 250200018 / 270001081 | Mounting and damping; choose the reference and position of the mount. |
 |
MAP Intake Pressure Sensor | 420274057 | Intake pressure measurement; stated 400 application, compare with the original reference. |
 |
O2 Lambda Sensor | 707600872 | Exhaust oxygen measurement, for setups equipped with this sensor. |
 |
Fuel Pump | 275500996 / 275500850 ; Williams 06-0700 | Fuel supply; stated 400 application, compare 380 to 400 mm depth in the tank. |
 |
Sea-Doo / Williams Flush Connector | Unspecified | Freshwater connection; choose the variant corresponding to the flush port. |
 |
Fuse Box Contacts, pack of 80 | No individual OEM reference | Electrical repair; check shape, locking, and electrical characteristics. Williams gasoline pin after 2019. |
 |
Jet Pump Impeller Shaft | 267000388 / 267000581 ; cross-reference SD-17 | Power transmission to the impeller; stated 400 / 460 / 520 application. Confirm reference and dimensions. |
 |
Steering / Reverse Cable Clamp Kit | 277001729 / 277001627 / 277000784 / 277000052 ; 277000055 ; 211100009 | Cable passage retention and sealing; stated 400 application, compare installation. |
 |
Fuel Injector Kit of 3 | 420874000 / 0280158383 | Fuel injection; stated 400 application, confirm flow rate, reference and calibration for the 125 HP. |
| Buy | Part | OEM Reference | Function |
|---|---|---|---|
 |
1503 4-TEC Head Gasket | 420641110 / 420950770 | Block / head sealing; Sea-Doo 130–260 HP fiche, validate 125 HP installation. |
 |
Valve Cover Gasket | 290950820 / 420950820 | Valve cover sealing; identify the cover and installed gasket. |
 |
4-TEC Timing Chain | 420898042 | Timing chain; engine reference to be checked for the 125 HP. |
 |
1503 Oil Pump Bellows | 420832648 | Oil system part; Sea-Doo 1503 part number, Williams mounting to be verified. |
 |
1503 Connecting Rod Bearing Kit | Unspecified | Bottom end rebuild; compatibility and STD or repair size to be determined by measurement. |
 |
1503 Intake / Exhaust Valve | 420254682 ; 420254293 / 420254298 | Targeted replacement; intake or exhaust, dimensions, ports and keys to be compared. |
 |
1503 Valve Stem Seals | 420630200 / 420630202 | Sealing around the stems; set of 6 or 12 depending on variant, cylinder head to be checked. |
 |
1503 4-TEC Magneto Stator | 420889721 / 420889720 / 290889720 | Electrical production; Sea-Doo 2002–2017 applications, Williams mounting and wiring to be confirmed. |
 |
1503 Complete Engine Gasket Kit | Unspecified | Sealing during a rebuild; content and BLACK / RED version to be validated for the installed engine. |
 |
4-TEC Forged Connecting Rod | 420917516 | Piston power transmission; reference and dimensions to be confirmed for the 125 HP. |
 |
Connecting Rod and Crankshaft Bearings | 420933456 / 420933466 / 420933523 | Bottom end rebuild; reference, affected ranges and size to be determined by measurement. |
 |
Intake Air Temperature Sensor | 420222427 / 420222423 | Air temperature measurement; Sea-Doo 4-TEC part number, Williams reference and connection to be compared. |
Common Problems with the WILLIAMS SportJet 400 – Rotax 1503
The following symptoms can have several causes. These clues guide checks, without replacing a diagnosis or automatically justifying the replacement of a part. Work on fuel, electricity and moving parts must follow the manual and be entrusted to a professional when necessary. (FMT)
- The engine does not start: battery, voltage during starting, battery disconnect, safety circuit breaker, fuses, relays, fuel supply, spark plugs, coils, injectors or sensors may be affected.
- Engine misfires: methodically check the ignition, fuel supply, sensors, wiring and compression before replacing a part.
- Lack of power: injection, ignition, cooling, electronic limitation or propulsion block may be to blame. A clogged water intake, damaged turbine or excessive play can reduce thrust.
- Fault code display: the code identifies a detected anomaly, but does not prove on its own that a part must be replaced.
To guide checks, consult our list of Williams and Rotax fault codes and our Rotax fault code guide. Stop the engine and prevent any restart before inspecting the water intake or propulsion block.
How to identify the right part for your SportJet 400?
Send us a clear photo, the visible OEM part number, the model, the year, the HIN number and the engine serial number. Specify the 125 HP Rotax 1503 engine and the presence of the iNR option for the components concerned. Do not rely solely on the SportJet 400 designation.
Identify my part from a photo.
WILLIAMS SportJet 400 Rotax 1503: Frequently Asked Questions - FAQ
-
What engine is fitted to the Williams SportJet 400?
The SportJet 400 of this generation uses a BRP Rotax 4-TEC from the 1503 family, a three-cylinder four-stroke engine of 1,494 cm³. Williams lists this version at 125 HP in its proprietary manual.
-
Does the SportJet 400 have the same Rotax 1503 as other Williams?
The Rotax 1503 has been used in different configurations and power ratings on several Williams Jet Tenders. However, peripherals, calibrations and certain part numbers may vary. Therefore, you should not order a part solely based on the "1503" displacement.
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What is the top speed of the Williams SportJet 400?
Williams lists approximately 71 km/h (44 mph). The actual speed may vary depending on the load, hull condition, boating conditions and propulsion condition.
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What is the weight of the SportJet 400?
Williams lists a dry weight of 520 kg.
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How many people can the SportJet 400 carry?
The SportJet 400 is designed for 5 people, with a maximum indicated load of 675 kg.
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What is the tank capacity?
The SportJet 400 has a tank of approximately 75 liters.
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Why won't my Williams SportJet 400 start?
The first elements to check include:
- battery and voltage during starting;
- battery disconnect;
- safety circuit breaker;
- fuses and relays;
- fuel pump;
- fuel pressure;
- spark plugs;
- ignition coils;
- injectors;
- engine sensors;
- fault codes recorded by the ECU.
An electronic diagnosis can prevent the unnecessary replacement of several components. (FMT)
-
Why does my Rotax 1503 start but lack power?
A loss of power can be related to the engine or the propulsion. The main clues are:
- spark plugs or coils;
- fuel supply;
- injectors;
- engine sensor;
- cooling problem;
- electronic limitation related to a fault;
- clogged water intake;
- damaged turbine;
- excessive play in the propulsion.
It is important to inspect the propulsion block before concluding that there is an engine problem. Stop the engine and prevent any restart before this inspection.
-
Why is my SportJet 400 overheating?
Overheating can notably be caused by:
- obstruction of the water circuit;
- clogged water intake;
- poor rinsing;
- damaged or clogged hose;
- cooling problem;
- defective temperature sensor.
If a temperature alarm appears, avoid continuing to use the engine before identifying the cause. See our article on engine overheating.
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Should the SportJet 400 be rinsed after every outing at sea?
Yes. Rinsing with fresh water is particularly important after use in salt water. Williams recommends notably rinsing the open cooling circuit and regularly cleaning the tender to remove salt deposits. Follow the applicable manual procedure; our engine rinsing guide is complete without replacing it.
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What is the carbon ring of the SportJet 400?
The carbon ring (or carbon ring, or carbon ring) is part of the transmission shaft sealing system. Its condition and that of the rubber bellows must be monitored. Williams recommends a professional check every 100 hours or before the season. An anomaly in this system can notably cause water to enter the engine compartment.
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Why is there water in the bilge of my SportJet 400?
A small amount of water can have different origins, but an abnormal accumulation must be investigated. It is advisable to check:
- the shaft sealing system (carbon ring, bellows...);
- the sea water / coolant exchanger (Ride plate)
- hoses;
- fittings;
- exhaust system;
- bilge pump
- a hole or crack in the hull.
The presence of water must be diagnosed quickly if it reappears after each use.
-
Why does my SportJet 400 cavitate on acceleration?
A sensation of cavitation or loss of thrust on acceleration may be due to:
- debris in the intake screen;
- a damaged propeller;
- a damaged propulsion unit
- incorrect clearance between the turbine and its surroundings;
- deterioration of propulsion unit components (see our article on wear rings);
- an air intake or water flow disturbance.
Inspect the propulsion unit before looking for an engine failure. Stop the engine and prevent it from restarting before inspecting the screen and the turbine housing.
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What oil should I use in the SportJet 400 Rotax 1503?
Use an oil that meets the specifications recommended by BRP for this engine: XPS 4T 5W-40.
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What spark plugs should I use on the SportJet 400?
The recommended spark plugs are NGK DCPR8E. Our compatible DCPR8E compatible spark plug is perfectly suited for the Williams 400 Sport with a 1503 engine.
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How do I identify the correct fuel pump, relay, or sensor?
Do not rely solely on the "SportJet 400" designation. To correctly identify a part, use the following whenever possible:
- the tender's year;
- the HIN number;
- the engine serial number;
- the part number marked on the original part;
- a photo of the part.
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Where can I find parts for a Williams SportJet 400 Rotax 1503?
Rotax Tender Parts offers engine parts and components for Rotax 1503 engines, notably used on Williams Jet Tenders. Find the selection in the tables in this article and view our Rotax parts catalog. Check the applications and part number of each product for your 125 HP engine.
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