How To Clean or Rebuild a Cafe Racer Carburetor

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In this post Bikebandit tries to help you to clean or rebuild a cafe racer carburetor by yourself.

A while back we touched upon how to tune a carburetor, but today we focus on how to clean out or rebuild a cafe racer carburetor.

Carburetors come in all different sizes and shapes but they all have a very important role in the mechanics of a motorcycle engine. Once gasoline enters your bike, it passes through the carburetor which infuses it with air in order to turn it into a fine mist before it enters the chamber where it is turned into energy. Unfortunately, this means that if anything other than gas or air enters into your carb, it’ll become clogged and your engine won’t get the gas it needs to run. With a clogged carb, you won’t be going far. Actually, you won’t be going anywhere. So it’s important to keep your carburetor clean and free of build up or gunk that can occur from having dirty fuel flowing from the gas tank.

how to clean a carburetor

Older motorcycles that have been sitting for a while will also need a good carb cleaning before they can be considered as good as new. If a motorcycle sits for a period of time with gasoline in its system, the lighter bases of the gasoline will evaporate leaving behind the heavier components of the gas. These heavier components will gunk up into a thick and annoying substance known as varnish that will keep your carburetor from doing its job. And if you do happen to be working on an older bike that hasn’t gotten much attention in a while, chances are that varnish build up won’t be your only problem. This is why so many people have to rebuild their carbs on older bikes. Luckily, the name of this task is a whole lot more daunting than the actual process itself. Rebuilding your carburetor is very similar to simply cleaning it except you’ll need to grab a rebuild kit. These Carburetor Kits will have the parts that your carb will need to have switched out. Just keep an eye out for corroded or broken parts to change out as you clean.

What You Need

Carb Rebuild Kit Nitrile Worx Performance Gloves K&L Carb Cleaner Kit Maxima Contact Cleaner Either way, it’s a pretty simple task (just don’t tell your friends that so that they’ll still be impressed when you tell them that you rebuilt your carburetor over the weekend). And to make it even easier, has tons of tools and kits, like this K&L Carb Cleaner Kit, to help. And you’ll definitely need to pick up a can or two of this Maxima Contact Cleaner. Of course, the first thing to do is to remove your carburetor from your motorcycle.

Removing your Carburetor

Taking your carburetor out of your engine will be a whole lot easier for some than for others. If you’re lucky, all you’ll need to do is start by slapping on a pair of these Nitrile Worx Performance Gloves. Working with your carb can be a bit messy, especially if you still need to drain it of gas. In order to empty out the majority of the gas in your system, shut your petcock switch to off (if you have a fuel injected engine, ignore this) to cut the gas flow off. Start your engine and jet it run for a minute or so before twisting your throttle a few times. You’ll know that you’ve gotten most of the gasoline out when your engine sadly sputters to a stall. Of course, there will still be gas in the float bowls but we recommend that you drain it after you’ve removed the carburetor.

The next step is to remove the gas tank, seat and side covers for easy access to your carb. With newer motorcycles, you’ll find that the rubber boots from the carb to the motor should be fairly easy to work with. Unfortunately, this won’t be the case for many older bikes. Loosen the circle clamps on all of the rubber boots or even take them off. If you have rubber boots that aren’t very pliable, taking them off might just get them out of the way completely. Either way, be careful not to bend them too badly as to not damage them.

Once you’ve got the rubber boots loosened and pushed out of the way or taken off completely, take a gander at your airbox. If you feel like you’ll need more room to detach your carburetor and your airbox is bolted down to the frame of your motorcycle, you can take out these bolts to give your airbox more room to move out of the way. At this point, you should have pretty good access to your carburetor, which should allow you to pull it out. You should notice that there is a throttle cable, fuel line, overflow and vent hoses all connected to the carburetor. Before detaching them, take note of how they are routed. Sometimes it can be a bit confusing when you try to reconnect them all after you’ve cleaned your carb. We even find that it helps to snap off a few pictures of them before disconnecting them just in case.

Once your carburetor is pulled out, detach all of the cables and fuel lines. Be careful of spilling gasoline. Even though you did shut off the petcock and run your engine dry, there will still be some residual gas in the fuel lines. With the carb separated from your bike, it should be easier to drain the rest of the gasoline from your float bowls. Grab a bowl or bucket to put under your carb and pull the drain pin. This should allow the rest of the gas that is in the float bowls to drain out which should leave your carb fairly dry.

The Take Apart

Once your carburetor is out of your engine and drained, you’ll need to take it apart piece by piece to get everything clean and check if anything needs to be replaced. This is the part that can turn a carburetor rebuild from an easy Saturday task to a nightmare. Be sure to pay attention to where you are taking parts out of in order to put them back in the right place. Especially if this is the first time that you’ll be getting a peek at the inner workings of a carb, it may help to have a notebook to help you write down and remember where parts go. (Our secret is using a digital camera to snap of pictures as we go as well.)

The first thing that you’ll want to remove from your carburetor is the float bowl. In order to do this, unscrew the four screws holding it on and set them aside in a safe place. Give the bowl a good tap with the end of your screw driver until it drops off or you can lift it off. You may find that it will stick depending on how dirty the inside of the carb is. Once it’s off, you’ll be able to get a good look at how much gunk has built up inside your carb and size up how much elbow grease and carb cleaner you’re going to need.

Next, remove the bowl drain screw and check the washer. These have a tendency to wear out and it may need to be replaced. Generally, you’ll rarely need to take out the carburetor’s float unless something has broken within your carburetor. If you do, check your service manual as there are tons of small bits and pieces that may need to be cleaned or replaced.

how to clean a carburetor 1

The carburetor contains many small jets, typically made of brass that also will need to be cleaned thoroughly. Any part with a small hole in it is usually dubbed as these and, depending on the model of your carburetor, there can be 2, 3 or 4 of them. If the tops of these parts have a hex shape, they’re screwed into your carb and will need to be unscrewed in order to be cleaned. If the top is round, the jet is pressed in and will usually have a small leaf spring keeping it in place. If you’re rebuilding the carb, many kits will come with replacements for these, which will allow you to throw the old ones away and skip the pain of having to clean the old ones. Soak the jets in carb cleaner to break down most of the grime that builds up on them. You’ll also need to make sure that the tiny holes are clear of anything. Try looking through the hole to see if you can get a clear view through it. If you can, the jet is clear and you’ll only need to get any residue build off of the rim of the hole.

how to clean a carburetor 2

If you can’t see through it, there are a number of things that you can do into order to clear it up. First, do the simplest thing: soak it in carb cleaner. Often times, this will be enough to knock free any gunk. If this still doesn’t work, try using an air compressor hose to blast the gunk out. Just be careful to keep a good handle on your jet as to not shoot it across the room. If this still doesn’t work, use the K&L Carb Cleaner Kit by selecting the right size wire and pushing it through the jet to push out gunk. Just be gentle as not to damage the jet. how to clean a carburetor 4If none of these tips work to get out the clog, you’ve really only got one option left: boil the heck out of it. By plopping that annoying jet into a pot of boiling water and letting it bounce around for a while, you’ll not only have a good chance of knocking out the rest of the build up as well as satisfying your frustration. After you take out the jet, you can use an air compressor again to clean it all the way out.

After you’ve removed and cleaned the jets, you’ll notice that there are brass tubes located under where the jets sit in your carburetor. This is the jet holder, which makes sure that the jet is in the right place at the right time in order for the fuel and the air to mix and turn into the vapor needed in the combustion chamber. To clean it, flip your whole carburetor over and remove the jet holders by pressing on the ends of it with a wooden dowel rod. Once they’re fee, soak them in carburetor cleaner and make sure all openings are free of gunk.

Unfortunately, you’re not quite done cleaning out your jets. We just had to save the worst for last. The pilot jet, or slow jet, controls the amount of gas that is released when the engine is in idle and tends to be in the worst shape when it’s pulled from the carb. This little guy hides under a rubber plug and can be screwed out by its slotted head. In order to have a smoothly idling carburetor, you’ll need this jet to be super clean. If you have a hard time getting all of the residue off, try all of the steps that you went through with the other jets as well. But if you can’t get the pilot jet to open up even after all of that, you may just have to buy a whole new one. has a whole slew of OEM Parts including pilot jets, as well as plenty of universal carb pilot jets.

Your carburetor has an air screw that works with the pilot jet to regulate the amount of air is mixed with the fuel during an idle. This part is typically located on either the side of the carb or on the bottom of it. To remove it, gently unscrew it and there will be a spring, metal washer and a rubber washer. Check to see if these need to be replaced and then set them aside before cleaning off the air screw.

Your throttle is what tells your carburetor how much fuel to feed to the engine. You pull you throttle and something called the throttle slide allows more fuel in. With a CV carb, you’ll need to remove the four screws at the top of the carb and remove the throttle slide. There will be a rubber diaphragm there that you’ll need to check for damage. If you see any tears, you’ll need to replace the entire slide. If not, just clean it with carb cleaner. Protruding from the bottom of the slide should be a needle, also known as the needle jet, and fits into the main jet holder. This will also need to be cleaned and check for any nicks or rivets.

how to clean a carburetor 5

With a slide carb, your throttle slide will most likely still be attached to the cables on your bike. This part will still need a good cleaning before you attach it back on your carb. Once you’ve wiped it and the needle down, detach it from the cable and put it back into your carb to see if it slides smoothly. If the slide still won’t move smoothly, try cleaning it with 0000 steel wool and clean out the inner wall of the carb as well.


The Clean

Your carburetor should now be fully emptied out of all of its bits and pieces. With it naked, there are a few ways to clean the body of your carburetor depending on how much varnish is caked on. One of the easiest ways it to just soak the whole unit in a bucket of carb cleaner until most of the grime has been broken down and then wipe it down. However, carb cleaner can get a bit spendy so you can use the extra elbow grease in order to spray contact cleaner on your carburetor shell and scrub the grime free with a towel.

Be sure to get all of the holes and passage ways. We recommend doing this over some sort of towel or catch can to keep the cleaner from leaking out of holes onto your floor. If your carb was in pretty bad shape, it might not be a bad idea to use your air compressor to blast air through to clean out passageways. If the air doesn’t go all the way through, it could either be because of a clog of because the passageway is a dead end. Be sure to double check and clean out the clog if it is one.

The Reassemble

If all of your bits and pieces, including the carb body, are clean, reassemble away. This is the point in which you might be glad to have paid attention to the disassembly of the parts or taken pictures of the steps as well as kept them organized. If you’re rebuilding the carb, replace the only parts such as the jets with the new ones that are in the kit.

It seems like there are a few things that tend to cause issues across the board during carburetor reassembly. For one, you’ll want to double check that the gasket for the CV slide diaphragm is in the right groove. Jets can also be troublesome and you’ll need to pay attention that the holders are pushed fully into place and seated correctly and that the jets themselves are firmly in place with the pilot jet completely screwed in. When replacing the air screw, be sure to also replace the washer, spring and rubber washer (which you may have needed to switch out for new ones even if you aren’t doing a carb rebuild) are also in place. In order to make sure your air screw is allowing the proper amount of air, screw it in all of the way and then screw it back out a few times. You’ll want to check your service manual to see how far the screw should be screwed back out but if you happen to not have one, the general rule is to unscrew it 1 1/2 to 2 times. Finally, be very sure that the bowl gasket is in place.

Once everything is back together, you might need to do a few quick adjustments. If you have a slide carburetor, you’ll need to adjust the idle screw on the side of the carb so that it barely touches the slide. If your carburetor has brass floats, be sure to adjust them to the specs in your manual.

One thing to note is that, when there’s more than one carb involved, you will need to synch them after cleaning them. That’s a whole other topic in itself and can be very technical and daunting. If you decide to take on that task, has a selection of carburetor synchronizer tools. Use a carb synchronizer, your motorcycle manual and probably the help of a local mechanic and, with the help of patience, you’ll be able to get it done!

If you don’t have to synch and your carb is back together, just plop that carburetor right back into your engine and hook it back up to all of the lines and hoses. Once you start your bike back up (remember to throw the petcock back into the on position, of course) you’re carburetor will give your engine a whole cleaner run for its money. And then you can brag to your friends about the insanely difficult tune up you did all by yourself.


Building a Cafe Racer Yourself?

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