If you've just picked up a Sito Plus exhaust for your scooter, you've probably noticed that the sito plus drossel is holding back all that extra "oomph" you were hoping for. It's a common situation—you buy a performance exhaust that's designed to look like the original part (the classic "sleeper" look), but out of the box, it feels almost as restricted as the stock pipe. That's because these exhausts are usually sold with a restrictor, or "drossel," to keep them street-legal and compliant with noise and emissions regulations.
If you're using your scooter on private property or for racing, you're likely looking for a way to let the engine breathe properly. Taking that restrictor out is usually the first thing people do, but if you've never done it before, it can be a bit of a head-scratcher.
What exactly is the Sito Plus drossel?
Basically, the sito plus drossel is a small metal cone or a washer that's spot-welded into the manifold of the exhaust. If you look into the end of the pipe—the part that bolts onto the engine cylinder—you'll see it right there. It looks like a little funnel that significantly narrows the diameter of the pipe.
The logic behind it is simple: by restricting the flow of exhaust gases, the engine can't rev as high or produce as much power. This keeps the scooter within its legal speed limit (like 45 km/h in many European countries). For the manufacturer, it's a way to sell a performance-oriented pipe that still gets an "E-pass" or homologation. Once you remove that restrictor, however, the exhaust is technically no longer street-legal in many jurisdictions, so that's something you've got to keep in mind.
Why people love the Sito Plus
Before we get into the nitty-gritty of removing the drossel, it's worth mentioning why this pipe is so popular in the first place. Most aftermarket exhausts for 2-stroke scooters look like big, shiny "expansion chambers" with a separate silencer. They scream "I've tuned my bike!" from a mile away.
The Sito Plus is different. It looks almost identical to the standard black box exhaust that comes from the factory on a Piaggio, Gilera, or Yamaha. It's quiet, it's discreet, and it doesn't attract unwanted attention. But once that sito plus drossel is gone, the internal design of the pipe allows for much better scavenging and power delivery, especially in the mid-range. It's the perfect choice for someone who wants more speed without the loud, buzzing sound of a racing pipe.
How to get the restrictor out
Now, let's talk about getting that little bugger out of there. It's usually held in by one or two small spot welds. You don't need to be a professional mechanic to do this, but you do need a bit of patience and the right tools.
The Dremel method
This is by far the cleanest way to do it. If you have a rotary tool (like a Dremel) with a small grinding attachment, you can carefully grind down the spot welds holding the sito plus drossel in place. Once the weld is thin enough, you can usually pop the restrictor out with a flat-head screwdriver or a pair of needle-nose pliers. The advantage here is that you don't risk denting the manifold or leaving jagged edges that could mess with the airflow.
The "Old School" hammer and screwdriver method
If you don't have a Dremel, you can go the more "brute force" route. You'll need a sturdy flat-head screwdriver and a hammer. You place the tip of the screwdriver against the weld and give it a sharp tap with the hammer. The goal is to "crack" the weld.
Be careful here, though. You don't want to deform the pipe itself, and you definitely don't want to drop the restrictor down into the main body of the exhaust. If it falls inside, you'll be shaking that pipe like a maraca for an hour trying to get it out.
Finishing the job
Once the drossel is out, I always recommend taking a small round file and smoothing out the area where the welds were. Any little bumps or sharp bits can create turbulence in the exhaust gases. It might seem like a small detail, but when you're dealing with a 50cc or 70cc engine, every little bit of flow counts.
Don't forget the carburetor tuning
This is the part where a lot of people mess up. If you remove the sito plus drossel, your engine is going to be able to push out a lot more exhaust gas. This means it's also going to want to pull in more air and fuel.
If you just remove the restrictor and go for a ride, your engine will likely run "lean." This means there's too much air and not enough gasoline in the mix. A lean engine runs hot, and if you're not careful, you could end up with a seized piston.
Usually, you'll need to increase the size of the main jet in your carburetor by about 5% to 10%. For example, if you have a size 60 jet, you might want to try a 64 or a 66. You'll also want to check the color of your spark plug after a short run—if it's white or light grey, you're too lean. You're aiming for a nice "chocolate brown" color.
Adjusting the CVT (Variator)
Removing the sito plus drossel changes the power band of your engine. The Sito Plus usually likes to rev a bit higher than the stock pipe to make its peak power. Because of this, your stock variator rollers might be a bit too heavy.
If the scooter feels sluggish when you're pulling away or seems to "bog down" before it starts accelerating, try putting in slightly lighter rollers. This allows the engine to get into the higher RPM range faster, right where the unrestricted Sito Plus starts to really shine. It's a bit of trial and error, but that's half the fun of tuning, right?
The sound and feel after removal
Once the sito plus drossel is a thing of the past, you'll notice a difference immediately. The sound becomes a bit deeper and "crispier," but it stays very manageable. It's not going to wake up your neighbors at 6:00 AM, which is a big plus.
Performance-wise, you'll likely see an increase in top speed—maybe 5 to 10 km/h depending on your setup—and the scooter will feel much more responsive. It won't feel like it's "hitting a wall" anymore when you reach a certain speed.
Is it worth it?
In my opinion, definitely. The Sito Plus is a great exhaust, but keeping the sito plus drossel inside is like buying a sports car and never taking it out of second gear. It's a relatively simple modification that unlocks the true potential of the pipe.
Just remember to be smart about it. Check your local laws, make sure you tune your carb properly, and don't go full throttle everywhere if you're trying to stay under the radar. Tuning is all about balance, and once you get the restrictor out and the jetting right, you'll have a much more enjoyable ride.
It's one of those "weekend projects" that doesn't cost much but gives you a very satisfying result. Just grab your tools, take your time with the welds, and enjoy the extra power. Just don't blame me if you start wanting to upgrade everything else on the bike next! It's a slippery slope, but a fun one.