Mikuni BN40I Carburetor Carb 270500328 for Sea-Doo Sportster Challenger GS GTI GTS 717 720

Mikuni BN40I Carburetor Carb 270500328 for Sea-Doo Sportster Challenger GS GTI GTS 717 720

This carburetor is engineered as a direct replacement for the Sea-Doo Sportster Challenger GS GTI GTS 717 720. Manufactured to meet or exceed OEM specifications, it delivers reliable performance in demanding conditions. Each unit is tested for fuel flow, pressure rating, and durability before leaving the factory to ensure consistent quality across every order.

Vehicle Compatibility

Signs You Need a Replacement

If your equipment is showing any of these symptoms, the carburetor may be the cause:

• Engine floods easily — The float valve isn’t seating properly, allowing fuel to overflow into the bore. The engine loads up with fuel and won’t start until it clears.
• Lean surging at cruise speed — A blocked main jet or partially clogged passage causes the engine to run lean under steady throttle. It surges as the mixture alternates between lean and rich.
• Black smoke and rich smell — Too much fuel relative to air. Check the choke mechanism, float level, and jet sizes if the carburetor has been modified.
• Fuel dripping from the carburetor — A worn needle and seat or stuck float allows fuel to overflow. This is a fire hazard and should be fixed immediately.
• Hard starting when cold — The choke circuit may be blocked or the enrichment valve stuck. Cold-start problems on a carbureted engine almost always trace back to the choke.
• Inconsistent idle speed — The idle mixture screws may need adjustment, or there’s a vacuum leak at the carburetor base gasket.

Rebuild Tips

Before installing the new carburetor, clean the manifold surface and check the gasket for any damage or vacuum leaks. Set the idle mixture screws to the baseline position (typically 1.5 turns out from fully seated) before starting. After starting, warm the engine to operating temperature, then fine-tune the mixture screws for the highest smooth idle. Adjust the idle speed screw last. If the engine backfires through the carburetor, check the valve adjustment and ignition timing.

Frequently Asked Questions

Will this fit my Mikuni 717?
Yes. This part is designed to fit the Mikuni 717, 720 among other models listed in the compatibility table above. Verify your specific model and engine code before ordering to ensure the correct fit.

How do I check if my engine code (BN40I) matches?
The engine code is stamped on a metal tag attached to the engine block, usually near the timing belt cover or on the cylinder head. Compare the code you find with the list above. Engine codes are 3 to 6 characters long.

Should I rebuild or replace the carburetor?
If the throttle shaft has lateral play or the carburetor body is warped, replacement is the better option. A rebuild kit handles gaskets, jets, and needles but can’t fix mechanical wear. For most applications, a new carburetor costs about the same as a professional rebuild when you factor in labor.

What tools do I need to install this on a Mikuni?
Standard metric hand tools will handle most of the job – sockets, wrenches, and a torque wrench. For Mikuni equipment, check the specific service manual for any special tools or torque values.

You May Also Need