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What do RFI and DI Mean on a Sea-Doo? [Explained]
In the 2000s, Sea-Doo offered its 2-stroke PWCs with three different engine options:
- Carbed Rotax: Carbureted twin engine with single or dual Mikuni carburetors
- Rotax RFI (RFI = Rotax Fuel Injection): Semi-direct injected twin engine (787cc)
- Rotax DI: Direct orbital injected twin engine (951cc)
We at JetDrift have compiled all you need to know into this Sea-Doo RFI vs. DI vs. Carb comparison post!
Carbureted Sea-Doo Engines
From 1988 through 1997, Sea-Doos were exclusively available with carbureted 2-stroke power sources.These 2-cylinder in-line engines featured single or dual Mikuni carburetors depending on the model.
In a nutshell, the most common carbureted Sea-Doo engines were as follows:
| Engine | cc |
|---|---|
| "Yellow" 587 | 580 |
| "White" 587 | 580 |
| 657 | 650 |
| 657x | 650 |
| 717 | 718 |
| 787x RAVE | 786+ |
| 787 RAVE | 782 |
| 947 RAVE | 951 |
Carbed 787 and 947 R.A.V.E. engines produced plenty of power but required more attention due to the R.A.V.E. exhaust power valves.
Moving on, let’s take a close look at fuel-injected 2-stroke Sea-Doo engines as well!
What does RFI Mean on a Sea-Doo?
Simply put, RFI means “Rotax Fuel Injection.” This semi-direct fuel injection system was designed to inject fuel into the low-pressure side of the engine. Therefore, RFI engines didn’t utilize carburetors, as their cylinders were already being fed by the injectors.Key components of the Rotax RFI system were as follows:
- Injectors
- Fuel rail
- Fuel pump in the tank
- Fuel lines
- Sensors
Since the RFI engine lacked carburetors, it required less attention and care.
On the other hand, the high-pressure fuel injection system added a lot of complexity to the engine. Because of this, working on the engine required special tools and expertise.
The Rotax 787 RFI debuted in the 1998 Sea-Doo GTX RFI. This model was followed by many other popular RFI models manufactured around the Millennium.
The exact list of Sea-Doo RFI PWCs included:
The main idea behind fuel-injected PWC engines was to reduce pollution in order to comply with the new, stricter environmental rules.Unfortunately, RFI engines weren’t significantly less polluting than their carbed counterparts.
This is why manufacturers tried switching to “real” direct injection systems, which pushed the industry towards less polluting and more fuel-efficient jet skis.
What does the DI Stand for on Sea-Doos?
The “DI” label on a Sea-Doo refers to its orbital injected engine. The only Sea-Doo DI engine was the Rotax 947 DI rated at 130 HP. Unlike its RFI counterparts, this 951cc 2-stroke twin featured both a fuel and an air injector. Therefore, the DI was considered to be a “true” fuel injection system that utilized a secondary system to atomize the fuel and inject it at the top of the cylinder heads.Although the fuel pressure was almost identical in RFI and DI engines, the latter used compressed air. To produce this, the 947 DI engine was equipped with an air compressor, which atomized the fuel and boosted its pressure up to around 110 psi.
This high pressure was required because the DI system injected fuel on the high side of the engine, so the injector had to overcome the combustion pressure in the cylinder.
In other words, the injector sprayed the fuel at the top of the cylinder after the piston had closed the exhaust port.
Thanks to this design, fresh fuel was kept in the cylinder and didn’t “escape” through the exhaust ports like on carbed and RFI engines.This advanced operation resulted in the most fuel economy in the 2-stroke PWC category along with the lowest fuel and oil consumption.
Drawbacks?
There’s no question that Sea-Doo’s DI engine was the most complex 2-stroke PWC engine in history.
It featured several components, including a fuel and air pump, a recirculation system with control valves, regulator, fuel rail, injectors, fuel lines, and so on. These units were prone to malfunctioning and hard to repair or replace.
The system was also very picky about battery voltage, just like fuel and air pressure. What’s more, it even required fully synthetic 2-stroke oil, which was expensive.
Sea-Doo marketed only a few DI jet skis from 2000 through 2004, which were as follows: The Rotax 947 RFI RAVE was also available in a simpler dual-carb version, which offered about the same performance.Conclusion: Sea-Doo DI vs. RFI vs. Carb
When it comes to the Sea-Doo DI vs. RFI vs. Carb debate, it’s safe to say that the carbureted engines were by far the most reliable choices.The RFI engine offered less reliability and durability, while the DI was definitely the worst of these three.
Therefore, if you are considering buying a vintage 2-stroke Sea-Doo, you may want to invest in a carbureted model. They are not only far more reliable but much easier to troubleshoot and service.
If you decide to stick to fuel-injected 2-stroke Sea-Doos for some reason, it’s highly recommended that you steer clear of the DI models.
Fixing Sea-Doo’s DI engine is hard to impossible, while its components come with hefty price tags (if available at all).
If you have strong mechanical skills and are looking for a challenge, your option could be RFI models, which are halfway between the carbed and DI engines.
As a takeaway, we’ve compiled the pros and cons of DI, RFI, and carbed Rotax engines:Carbed
Pros: Simple design, easy to work on (even at home), fewer and cheaper components, aggressive acceleration, and requires cheaper oil
Cons: Higher fuel and oil consumption, and requires frequent “carb work”RFI
Pros: Better fuel and oil economy, smoother throttle response, slightly lower pollution, and no “carb work”Cons: Less aggressive acceleration, complex design, harder to work on, and requires fully synthetic oil
DI
Pros: Class-leading fuel and oil economy, lower pollution, smooth operation, and no “carb work”Cons: Lower reliability, very complex engine with a lot of special components, extremely hard to fix, expensive and hard to find components, (not recommended to buy!)
