Cleaning the carbs 1

Intro to carb cleaning

If you clicked on this page thinking you were going to find some miracle product you could pour in your gas tank that would solve all your carburetor woes, you were mistaken. There is really no substitute for removing the carbs from the bike and giving them a proper hand cleaning.

The older formula of Yamaha Carb Cleaner used to be recommended in this space, but it is no longer available. Its replacement, also called Yamaha Carb Cleaner, is a water-based product that is less effective than the original. If your online store shows a bottle like the one on the left, they're using an old picture. The newer stuff looks like the right photo.

The Yamaha Cleaner's main usefulness was always for loosening the crud inside the carbs, making the later (and necessary) hand cleaning a lot easier.

Pre-soaking, for really gooped-up carbs

Berryman Chem Dip method

loudboys says that Berryman Chem Dip is the best carb cleaner on the planet. It comes in a gallon can; basically a paint can with an included basket to put the parts in and lower them into the can. He's been using it for 25 years. You can take a carburetor that's been sitting in a junkyard for decades and clean it in an hour. The really great thing about it is that after you're done, you put the top back on and use it again later. A can of it will last for years.

Notice: You have to keep all rubber and paint well away from it (including rubber o-rings, diaphragms and seals). Hard plastic parts won't be affected. You'll want to wear gloves when you use it.

Stuff you need and need to know

Before you get started, take a look at the instructions for removing the carbs. If you can't follow the FAQ to remove the carbs, then you probably aren't equipped to clean them.

Chemicals

On the far right is a container of parts cleaner by Next Dimension. There is also a small amount in the Ragu glass jar on the far left. Next Dimension is highly recommended. Next to that is specific Carb Cleaner, by the same company. Spray cans of brake/parts cleaner work just fine as well. You DO need a spray can for this work. The last item, the open funnel/measuring cup, is the old Yamaha Carb Cleaner. Notice that it went from clear to green. It did its job.

Tools

A #2 phillips, assorted flat blade screwdrivers and a length of copper wire. Not shown is the #4 allen used to put back the replacement screws. The copper wire is essential for reaming the passageways and helping clean. Any metal more aggressive than copper has a very good chance of hurting the carb internals and making them not operate correctly. If you just mess up jets, well that's a $5~7 per item mistake, but if you scratch a passageway, then you're looking at a new set of carbs. And it's essential in the same way a toothbrush is, vs. just rinsing with Listerine... you need to scrub the tough bits that are stuck.

One important thought with regards to working on an engine is that any time you leave an opening to the engine you should block it. If you don't, then Murphy's law will just help you drop something inside. Paper towels are cheap and effective.

It's VERY important that you use a quality screwdriver that's the right size and in good condition. If you don't, then you're going to bugger up the screw and cause yourself more headaches than just buying and using the right tool in the first place. The screws on carbs, brake reservoirs and the 250 bar ends are notorious for being stiff to remove. Don't let something like this happen to you:

A note on screwdrivers: Motorcyclist magazine, in its May 2007 edition, had a tech tip for Japanese carburetor screws. Take a close look at the photo above while you read this. This is quoted directly from the magazine, and no one from the board has tried these products, but we do consider this a reliable source:

• It is quite often difficult to get the Phillips screws out of the carburetor float bowl. Those and a lot of other screws on Japanese products... are specifically Japanese Industrial Standard JIS 4633B-3/1991 and DIN/ISO standard 5260. Note the dot in one corner of the cross formed by the slots... The Japanese-style Phillips screwdrivers are available from Ames Supply Company and Katun... Using the normal American/European #1 or #2 Phillips screwdriver in a screw head with the dot on it will most likely strip the head on the first try.

A couple other options for float bowl screw removal:

• Take a Dremel and cut slots in the screws, then use a flathead screwdriver to remove the ridiculously soft metal screws. You may have to cut a piece off of the idle adjustment bracket to get at one of the screws.

• Another, most likely easier, suggestion is to (carefully) put the carbs in a bench vice and remove the screws with an impact driver, BEFORE you strip them. Whatever you do, plan on replacing the float bowl screws with allen-headed ones.

• Another trick: As long as you're going to replace them anyway, use vice grips. By gripping the screw top down and holding it hand tight (not clamping) then twisting, it should make a popping sound as it breaks free. As soon as it pops, stop twisting, get a phillips, and turn the screws out.

• One more: Drywall driver bits are great for JIS screw heads. Available at your local Home Depot or Ace Hardware. Whoever designed the drywall bit gave us a perfect JIS screwdriver substitute. They come in various sizes and they're cheap.

Carb parts

The following are the different parts of a carb. Note that not all carbs look exactly the same. These are NOT EX250 carbs, and not even Keihins, but most carbs are similar to these.

This is a picture of the float. It's what controls the level of fuel in the carbs:

The floats do this by floating (duh?) on top of the gas and pushing the fuel needle against its seat. The fuel needle (shown below) should be inspected to ensure that the rubber tip is a well defined cone. If there's a dish in the middle, that means it's worn out and needs to be replaced. Worn needles will leak fuel into the carbs, which will then leak into the engine and flood it, as well as leak past the rings and contaminate the oil. Just a whole ball of wax best to avoid:

This is the main jet:

The pilot jet:

And the enrichener (choke) pickup:

For more views of these parts, see Carburetor photos.

The cleaning process

Remove all of the above items prior to cleaning, except the enrichener pickup; that's part of the carb body. This should leave you with just an empty looking float bowl (well, the top of that chamber, bottom of the carb itself). This is the 'meat' of the carb. Up top is just the slide and needle (which will be touched on later in this article). You need to probe each and every hole with some wire. Twist a few strands together for the big holes, and just use 1 piece, slightly kinked up, for the smaller holes. You want to be sure to get ALL of the holes, like these on the side of the pilot jet:

The pilot circuit, also called the slow speed circuit, has the smallest holes/passages. They are the first to clog and are deserving of the majority of the attention. The pilot circuit outlet:

And the transition outlets. These allow for more fuel to enter the engine than just the pilot and help smooth the transition to the midrange, which is controlled by the needle. These aren't pointed to, but are visible just under the brass butterfly valve in the center:

Take the compressed cleaner and, using the straw, squirt fluid into every hole. You should have cleaner going into or coming out of each and every hole, though not all at the same time, and in the same volume as the other carb bodies. And it should be coming out clear (this one started greenish).

When it comes time to reassemble, the jets just screw back in, but you need to set the float height. Each set of carbs has a different recommended height (listed in the service manual for the given bike). If the floats hang too low, your bike can (and most likely will) run lean, and if they sit too high, you'll likely be fighting a rich running bike. The picture shows a special tool for measuring float height, but a 6" ruler, or even a basic set of calipers, can be used to measure the height. To measure, you want the floats to just be touching the fuel needle, which has a spring on it - you don't want to compress that. Most carbs can just be set upside down and the spring will hold the floats where they need to be; some carbs you'll need to tilt at an angle while doing the measuring. To adjust up or down, you just bend the small metal tang that rests on the fuel needle:

With that set, feel free to screw the float bowl back onto the carb. It's best to replace all the phillips screws with stainless allen screws, as they're easier to work with and aren't too expensive. Float bowl screw size is M4 0.7 pitch, with 14mm length. This is commonly written as M4x14 0.7, although you may want to bring your old ones with you, just to make sure. If you have to get slightly longer screws (say, 16mm) that will work fine.

Up on top you have a diaphragm that controls the speed at which the slide goes up and down via high and low pressures, which raises the needle, which directly controls the midrange fuel delivery. The needles are traditionally set a bit low to lean out the bike for EPA emissions. The most standard fix is to just put a couple 2.5 or 3mm washers on the bottom, so the needle is raised up a little from the start.

That's the only adjustment that can be made up top. Make sure that the diaphragm doesn't get damaged or pinched when you reassemble. The carbs won't work right, and they are expensive to replace! Test all the slides by just pushing them up with a finger and comparing them to banks you haven't touched yet, or just make sure they all react the same.

That's all there is for cleaning and adjustment inside the carb. There is one other adjustment outside of the carb, and that's the air/fuel mixture screw. This is the item that has the plug covering it from the factory, which is usually called an anti-tamper plug or "EPA plug". You need to drill a small hole in the plug, then screw a screw into it and pull the plug out. It's just a pressure fit. What you'll be left with is the screw that meters the air OR fuel for the pilot circuit. If the screw is on the engine side of the carb it meters the fuel; if it's on the airbox side it meters the air. Again, this is set to the lean side from the factory. By adjusting this screw, you can help cold start issues. A good base setting is 2.5 turns out from fully seated:

And that's it for what can be done on the bench. When you install the carbs again, do a carb sync.

Here is the full gallery of photos used in this write-up.