The Honda Ruckus Carburetor: Keihin NVK

The Honda Ruckus Constant Velocity Carburetor

The Honda Ruckus has been around since 2003 but the one thing that has been constant is that it uses a carburetor instead of fuel injection. Fuel injection has been a recent change in scooters, but even though the 2012 Honda Metropolitan is fuel injected, the Honda Ruckus is still using the Constant Velocity (CV) carburetor. Why is the CV Carburetor still used and what kind of Ruckus parts can we use to make it work better?

The Constant Velocity Carburetor is the OEM carburetor in the Honda Ruckus. It is made by the Japanese vehicle engine management company, Keihin, who has been in business since December of 1956. It started out as an automobile parts repair and processing facility and it wasn’t until September of 1957, when they started producing carburetors for the Honda Dream motorcycle and Fuji Heavy Industries Rabbit scooter. The carburetor model for the Ruckus is the NVK, but does use Main Jets for the FCR Carburetor. The FCR is a variable Venturi carburetor and not the same as the NVK, it is just that the Main Jets are. The Slow Jets come from a DVK Carburetor that is in Kawasaki V-Twin ATVs like the KFX-700 V-Force, which is a CV Carburetor and it may be a deviation of the Keihin CVK. It, however, does not use the same Main Jet as the FCR or the NVK.

Tuning the Ruckus carburetor is the same for any CV, Variable Venturi, or Fixed Venturi carburetor; you use the Plug Chop method and change your air/fuel mixture screw and main and pilot jets to tune accordingly. The only issue that arises is the difficulty to procure main jets at the time of this article. Keihin, for a reason not given to us, has not produced enough jets to keep up with demand. It is entirely possible that the main cause is a switch by many motorcycle manufacturers to fuel injection. As stated before, Keihin is an engine management company; which means they also manufacture ECUs, fuel injectors, and other EFI (Electronic Fuel Injection) components. With the Metropolitan and Zoomer, the overseas name for the Ruckus, becoming Fuel Injected bikes, the demand for jets for the NVK carburetor is down in demand except for here in the North American Continent where the Ruckus is still a carbureted bike.

So, what can be done? There isn’t much, sadly I must report. Until those jets are produced by Keihin or another aftermarket manufacturer, there is not solution except custom modification. This means finding ways to shim the needle and/or opening or closing the main jet for the perfect fueling. Shimming the needle wouldn’t be too difficult and is easily reversible; however modifying the main jet would not be easily reversible. While we do not recommend, and highly request that you do not, do this modification, you can use solder to close up a main jet and drill it out to enlarge it. Again, we do not recommend this modification as once you perform it, you will never get the jets back to the way they were. Shimming the needle is easy and can be undone; the problem lies with finding a shim thin enough to work. Brass washers are very thin and could work, but I have no data to confirm this other than knowing this is how Harley Davidson CV carburetors are modified. They also use a Keihin CV carburetor, but the CVK is not the same as the NVK.

Honda Ruckus and Yamaha Zuma Stretching

If there is a common theme in Honda Ruckus Parts and Yamaha Zuma Parts, it is stretching the bikes out. However, how do they achieve that look? How is it really done and is there a purpose? What started this trend?

Stretching a scooter like the Honda Ruckus and the Zuma 125 isn’t very hard to do. Actually, the harder question to answer is where the trend originated. The common answer is that it started with the big bikes and their extended swing arms. Hill Climb Dirt Bikes, with their crazy big engine, nitrous fed, insanity used a stretched swing arm to overcome gravity and make the bike more stable going uphill with all of that crazy power. If not, they would probably end up going backwards far more often than up the hill. It also came from the drag bikes, with their longer swing arms to also overcome the power of the engine from lifting up the front of the bike as much as possible to keep it going with full throttle blasts. What it is doing is reducing the anti-squat of the rear wheel by decreasing the angle between the horizontal plane and the swing arm. It’s like changing the pivot point on a seesaw; the longer the unloaded end of the lever, the easier it is for the unloaded end to move the loaded end.

Some guys then saw the drag bikes and though, “hey, that looks cool!” Thus more and more street bikes began to stretch their sing arms to reproduce that same look. They weren’t after the gains in straight line speed, but just how the bike looked. Of course what happens in the big bike world also happens in the scooter bike world. Someone saw that big bike with its stretch and though, “I want me scooter to look like that!” Soon, from those custom jobs came the first stretch kits and the rest is history. Currently, there are many, many manufacturers of stretch kits for your Honda Ruckus, Yamaha Zuma, and even swapped engines. They range from stretches that look cool to guys who are hardcore about their drag racing scooters. They even range from weld to bolt in kits as well as from a couple of inches to over 12 inch stretches!

While it doesn’t matter how the stretch is achieved, the way a stretch is achieved on a scooter is the same from scooter to scooter. Instead of buying a longer swing arm, which is not possible in most cases on scooters, the engine, CVT, and wheel are all relocated towards the rear of the bike. However, just like their big bike cousins, many of the effects of moving the axle back are there. The bike will have less of a tendency to wheelie, it will be stable from mid-turn to straight, and won’t like tight corners. So, if you’re looking for a nimble scooter, you’ll want to stay away from most stretches. However, for you guys looking to maximize straight line speed and need something to help keep the front of the bike down as you accelerate, stretching the bike is something you should be looking towards. If anything, after making an engine choice, the stretch should be towards the top of the list of needed parts.

Honda Ruckus Essential Tools

Many people go buy a Honda Ruckus scooter and take it to the dealer for repairs or service to find out that dealer just charged them $90-110/hr for labor. That wallet shock has lead to many scooter riders to become scooter experts when it comes to their repair and service needs. Unfortunately they also find out the hard way on what tools they really need. This guide will take you through some of the Ruckus parts and tools you really need to make sure your next service doesn’t cost you much money or much time waiting on parts. Not only will you be able to work on your Ruckus, but you’ll become more familiar with it, too.

One of the very first things you should pickup is a Honda Ruckus service manual for your year Ruckus, though most manuals go from 2003 to present Ruckus scooters. You will want to get the Honda made service manual, the very same one Honda Motorcycle technicians use. Typically, most aftermarket manuals can miss a detail or two that can be required to know. This isn’t always the case, but it is always better to have the factory manual. These can be purchased at your local Honda Motorcycle dealer or at some of your local scooter stores. What is really nice about the Honda Factory manual is that it will show you the proper way to route cables so that it not only goes back in the factory position, but they will also be easier to deal with.

The next thing to make sure you have is a decent set of hand tools, which include socket wrenches, open-end/box-end wrenches (the wrench most people typically think of when you say “wrench”), screw drivers, pliers, and an adjustable wrench. When you do pick up your socket and open/box wrenches be sure they go from 8mm to 17mm, as these are the typical sizes of bolts and nuts on your Ruckus. A quarter inch drive socket set is a great starting point and will usually have socket sets in the 8mm to 21mm sizes. It’s big enough for good torque, but small enough to reach most anything on the Ruckus. However, if you are not careful it can still break a bolt or stud if you over tighten them. An eighth inch drive socket wrench is great for smaller bolts and nuts and tighter places, but there isn’t much on tight spaces on the Ruckus considering how open it is. You don’t have to necessarily splurge on Mac or Snap-On hand tools, as ones from Craftsman, Northern Tool, and Harbor Freight are of very good quality, too. Most all hand tools carry a lifetime warranty on them as well, so if they break, you can get them replaced.

There are a couple of final tool types to have that can be essential, the torque wrench and a good digital volt and ohm meter (also known as the DVOM). These are two tools that you should spend on getting excellent quality and will be something you want a name brand on. However, just like many things, price does not always guarantee quality but it is a good reference. You want to try and get two different torque wrenches: the inch-pound and the foot-pound. You’ll use the inch-pound on the smaller bolts and nuts while you will use the foot-pound on larger ones. The DVOM is essential to have because of the electrical parts you can run into on the Ruckus. You’ll want to also be sure that your DVOM can do AC (alternating current) and DC (direct current) power. Alternating current will come from your stator and charging system. Direct Current will come from your battery. The DVOM will allow you to check for things like open circuits (broken electrical wires or blown fuses), resistance, current, and voltage. Also learn about voltage drop as that can solve a majority of electrical issues on your Ruckus battery, especially on things like battery drain on a parked scooter.

The Engine: What Route Should I Go on my Honda Ruckus?

Everyone wants to go faster but the 49cc GET engine in the Honda Ruckus just isn’t fast enough. Sure it can get you to 40-43MPH, but that isn’t fast enough to keep up with traffic in most cases! That’s just not safe, especially with the increase in distracted driving cases and motorcycle crashes. So, what can we do? How can we pick up more speed after maxing out what the variator, CVT, and gearing changes did? Luckily, there are a couple of Honda Ruckus parts on the table and we’ll discuss them today!



The Honda Ruckus is quickly becoming the scooter to have to try and push to 50+MPH. The Honda reliability in the chassis and engine beckon tinkerers to make it faster. While not very common, increasing the bore of the Ruckus is starting to become popular; it offers great gains, but has some tradeoffs. The first tradeoff is time. The GET is a water-cooled engine and you have to take the cylinder off of the bike and take it down to a machine shop to bore out the cylinder to the size you need. Many machine shops are not capable of this because of how small the bore of the Ruckus is.

The next trade off is loss of reliability. With any upgrade, there is a risk of losing all reliability and it is especially so with the big bore upgrade to the GET engine. The final tradeoff is heat. With the big bore making the cylinder walls thinner, there is less area to shed heat from the cylinder, even with water-cooling. The oil also begins to heat up more, thus causing many failures in the engine.



If that puts you off of the big bore upgrade, there is good news in the engine swap arena. The Ruckus frame just begs to have something else in it. It is such a piece me together bike, it is no wonder people ask if you made it yourself. This is what makes the engine swap possible and slightly easier in the Ruckus versus other scooters. The most common is the Ruckus GY6 Swap, as the engine is cheap and plentiful. It is used in so many Chinese built scooters, you can find it anywhere. Even brand new, the GY6 is still inexpensive to purchase with most going for less than $500 out the door (but still would require a wheel made for the GY6). If you want the best wheel choices, you’ll want to get a long CVT case engine as it will allow for up to a 13” wheel with low profile tires.

Once you get the GY6 engine, you’ll have to choose how to mount it. There are many companies that offer GY6 swap mounts that range from inexpensive, normal tire weld-in mounts to completely bolt in 8” + fatty tire mounts. It’s really up to you which direction you’d want to go. As with anything, there are some tradeoffs that must be considered.



The first is that this is a Chinese built engine. This isn’t to knock everything Chinese made, but their reputation isn’t exactly great. Reliability may be an issue on a used engine and a little less so on a new one. Second, this will not bolt into the OEM GET engine mounts or even aftermarket GET mounts. It looks similar, but it is not the same as it is wider. Third, the GY6 engine, even the 50cc short-case version, will not hook up to the GET wiring harness without modification or a new harness. Finally, there may be some legal issues with a swap. If you have to smog test your scooter, then a GY6 swap may not pass as most of the GY6 swaps involve the 125cc and 150cc versions. The short case 50cc GY6 could possibly pass, but you will not be gaining anything in that swap other than an air-cooled engine.

However, don’t let this put you off of doing a GY6 engine or even big boring the GET engine. While each has negative tradeoffs, there is one positive tradeoff that overshadows them. That is the power you gain from a big bore or engine swap. The 125cc and 150cc GY6 engines are nearly capable of 60MPH out of the box and big bore GETs have shown anywhere from 55-60MPH. Whichever way you go, you will have a bike capable of beating most traffic on those surface streets.