Look, we’ve all been there. You just picked up a new classic Honda—this time it’s one of Team Red’s tiny, mighty twin cylinder 175 or 200 family of bikes—and despite your best efforts, it just won't run right. You dig a little deeper and, surprise surprise, you discover that the carburetors are a disaster. Don’t fret! Luckily for you, the little round slide carbs Honda used on the CB175 / CL175 / SL175 / CB200 / CL200 bikes are simple and easy to work on. So, let’s dive right in and get those carbs cleaned up, shall we?
Once you get the carbs off the bike, set them on the bench and have a good look at them. See how they’re not identical, but mirror images of one another? Keep that in mind, it’ll come up later when we reassemble everything. Oh, also, despite these carbs being pretty simple, they’re still full of fiddly little parts and springs that you need to keep careful track of. When taking them apart, do one carb at a time, keep your parts separated, and never get your slides mixed up. We’ll talk about that last part in a minute.
At the top of each carb where the throttle cable enters, there’s a big knurled ring screwed down over the carb body—that’s the top cap nut. It should be finger-tight (if not, you’ll need some channel locks and a little brute force to get it off), so unscrew it and pull the slide assembly out of the carb body.
The slide assembly—slide, slide needle, needle retainer, spring, gasket, top cap, top cap nut, and cable adjuster—comes out in one piece. To take the assembly apart, first wiggle the throttle cable out of its housing on the slide and set the slide aside. Remove the spring, top cap, and top cap nut. Next, remove the old, probably ruined gasket and cable adjuster from the top cap, and then slide the top cap nut off and set it aside.
Inside the slide, you’ll see the needle and needle retainer spring. Pop the retainer spring out, this can be done by pushing the needle up into the slide. Once complete remove the needle, noting which groove the little clip is in at the top. These must be the same on each carb and, if removed, replaced in the same groove you found them in.
We need to take a sec to talk about the slides here. Remember how I mentioned earlier that the carbs are mirrors of each other? That means that the slides have to be put back into the carb they came out of for the carb to work correctly. The way you can tell if the slide is in the right way is that the angled, cutaway half of the slide is facing the air cleaner while the flat side is facing the engine. If you get them backward, which is a common mistake, the bike will never run right and you’ll lose your mind trying to figure out why. Take it from someone with experience.
Once the slide assembly is out, you can split the carbs by removing the choke linkage. This is as easy as pulling the tiny cotter pin that holds the rod to the carb’s choke arm and removing the rod. This is, honestly, as far as you’ll want to go with the choke system on these carbs. There’s an internal choke mechanism, but it’s so hard to get to and so fiddly that unless the choke is somehow seized up in the carb body, you should just leave it alone.
At this point, if you haven’t already, remove the intake pipes. It’s as easy as removing the screws with your handy dandy JIS #3 screwdriver (you do have JIS screwdrivers, right?) and popping them off. Sometimes the rubber o-ring between the carb body and the intake is a bit sticky and the manifold sticks to the carb body. If this happens, just give the manifold a light tap with your screwdriver’s handle to loosen it.
Idle Speed and Idle Mixture Screws
Next, we’ll remove the idle speed screw and idle mixture screw. The former is a large-ish, flat-head screw with a knurled edge protruding from the center of the carb body, just above the float bowl clip mount. This screw fits into the larger slot in the slide and modulates idle speed by controlling how far the slide descends into the carb body. It should be finger tight, so you can just unscrew it and set it aside, but you may need a screwdriver if it’s really in there. Make sure you also get the little spring from inside the port while you’re at it. The spring should come out with the screw or fall out on its own, but if it doesn’t you can get it out with a pick or similar tool.
The idle mixture screw is located in a recessed port just above the float bowl and forward of the idle speed screw, close to the air inlet. It controls the fuel-to-air ratio by, in the case of these carbs, increasing or decreasing the amount of air mixed with the fuel at idle. Using a small flathead screwdriver, back the screw out of its port like you did with the idle speed screw. The idle mixture screw has a spring like the idle speed screw, so don’t forget to pull that out as well.
Two different idle mixture screws were used in these carbs—a solid screw and a hollow shaft screw. The solid screw completely shuts off airflow when screwed all the way in. The hollow screw has a horizontal hole drilled through the shaft about halfway down and a vertical hole drilled through the center of the horizontal hole, making a t-shaped air channel inside the screw. This air channel allows for a minimum air bleed through the idle circuit at all times, even when the screw is all the way in. Make a note of which style is used on your bike and make sure to replace it with an identical screw.
Float Bowl and Jets
Removing the float bowl and all the assorted needles, jets, floats, and pins it covers is the final big part of tearing these carbs down. Start by removing the drain plug from the float bowl using a broad flathead screwdriver. It should be snug but not terribly hard to get off, but sometimes the rubber o-ring around the plug’s shaft swells and sticks inside the drain, making removal kind of a chore. As with the idle mixture screws, there are two different drain plug styles used on these carbs—the early-style small plug and the late-style large version.
With the drain plug removed, pry off the spring clip that holds the float bowl to the carb body. Most of the time you can do this with your hands, but if the clip is stuck or jammed you can pry one end of the clip out of the carb body to make removing the clip easier. Once you get the clip off the float bowl should come away from the carb, exposing the float and jets. If its stuck on, just give it a light tap with a screwdriver handle to break it free. Once the float bowl is off, remove the old, worn-out float bowl gasket and toss it out.
With the float bowl off you have unfettered access to the float, float needle and seat, the jets, and the other bits of the carb that regulate the flow of fuel into the engine. Chances are these are pretty filthy and gummed up, so getting some or all of them out without damaging anything might be tricky.
Main Jet, Pilot Jet, and Emulsifier Tube
These solid brass fittings are screwed into threaded ports cast into the center of the carb body. The pilot jet, or idle jet, draws fuel from the float bowl at low RPMs while the main jet pulls fuel at middle and higher RPMs. Removing the idle jet is simple, you just unscrew it from its port using a flathead screwdriver. Removing the main jet involves an extra step, however.
The main jet is screwed into a brass fitting called an emulsifier tube, and then the tube is screwed into the carb body. For the best results when cleaning or replacing these pieces, you need to separate them. Thankfully, Keihin made it easy on us by using a 7mm hex into the top of the emulsion tube where the jet screws in. To remove the jet, hold the emulsion tube in place with a 7mm wrench then unscrew the jet and remove it. Then you can just break the emulsion tube loose with the wrench and spin it out with your fingers.
There’s a good chance the jet will be stuck in the emulsion tube, so spray a little carb cleaner on it and let the chemicals break up any varnish or corrosion to make removing it easier.
Float, Float Needle, and Float Needle Seat
The float, float needle, and needle seat work together to regulate fuel flow from the bike’s fuel tank into the carburetor. A stuck needle or a leaky or incorrectly adjusted float can starve a bike of fuel or cause it to flood and leak fuel everywhere, so proper care is important. Getting them out of the carb is a simple job, but one that can be complicated by a couple of factors.
The float in these CB175 / CL175 / SL175 / CB200 / CL200 carbs is a brass contraption that looks like two wheels of cheese connected by a vaguely t-shaped armature. It’s connected to the carb by a small pin that runs through the center of the armature and two towers cast into the carb body. Usually, all you need to do to remove the float is wiggle the pin out with a pair of needle nose pliers or, if you’re lucky, your fingers and lift the float out.
Many times, however, the pin is seized in place and you’ll need to apply a little force to get it out—a small punch and a hammer, for instance. Doing this can be exceedingly dangerous because if you get a little too aggressive you can snap one of the towers off the carb body and ruin it. What you can do in cases like this is to spray some carb cleaner on the ends of the pin to break up any varnish or corrosion holding it in place, then apply some penetrating oil to lubricate it.
If it’s still stuck fast and you can’t get it out with your fingers after soaking it, use a small punch and hammer to gently tap the ends of the pin until it breaks free. Slide it back and forth a couple of times to loosen it up, and then just pull it out. Once the pin’s out you can just lift out the float and set it aside for cleaning.
Needle and Seat
The needle and seat are the last pieces we need to remove, and they’re among the easiest to get out. Unless it’s completely stuck in the seat with gummy old varnish, the needle should just fall out in your hand if you tip the carb over. To remove the seat, just back it out with an 8mm socket.
Emulsion Tube Discharge Nozzle
Last, but not least, it’s time to remove the discharge nozzle. This small brass tube is press-fit inside the carb and the slide needle fits inside. To get it out, find a way to prop up the carb so it’s sitting the right way up—we used the flat surfaces of a vise, but you can use wood blocks, big sockets, or anything else you have lying around. With the carb propped up, use a punch and hammer to gently tap the nozzle out through the bottom of the carb. Once free, it’ll fall through the port where the emulsion tube and main jet were installed and you’ll finally be done tearing down your carburetor!
Once the discharge nozzle is out, take a close look at it. See how one end has a small, flat opening and the other has a wide opening with beveled edges? When you reinstall the cleaned discharge nozzle, or a new one if you’re going the full rebuild route, remember that the beveled opening faces up toward the slide and you’ll be good to go.
So, there you have it. You have your CB175 / CL175 / SL175 / CB200 / CL200 carburetor all torn down and ready for cleaning. In the next video, we’ll show you how to reassemble your freshly cleaned carb with new parts from our CB175 / CL175 / SL175 / CB200 / CL200 carb rebuild kits.