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Carbs 101


  • Carbs 101

    Carbs 101

    Carburetor Reference Guide for pre98 bikes.

    RULE # 1 is DON'T mess with things that you don't know anything about! (Take them to a pro & pay them to fix it)

    RULE # 2 is that if you ARE going to mess with things, get a reference or some education on what you are about to mess with! (Buy the book, read it and look at the pictures!)


    Failing all the above, at least try a logical approach to things:


    Check these in this order:
    • Run bike to warm +
    • Squirt water on the pipes. Does it sizzle? Or Run?

    (Sizzle = Running, Cool= not or little or no fuel getting thru it)

    Running, but rough? Could just be they need synchronized (AKA synch or synch'd) (Get a set of Motion Pro Carb sticks, the econo version, or a manometer. Do not use gauges.)

    If synching your carbs still won't make it run smooth, it's probably a mechanical issue inside the carbs.

    Removing the Carburetors

    Remove carbs from bike. Remove the choke cable and the throttle cable(s). Remove the idle adjuster cable. Remove the carbs WITH the air box ON the carbs. You may opt to remove it now if you know you are going to get deep into this……if you think this operation is going to be a minor one, leave them attached! (Note: If your clutch cable is routed between carbs 1 & 2 and between the carbs and the air box you will have to remove the air box to remove the carbs all the way from the bike. Reroute this cable to the LEFT of carb # 1 forever. This gets it outside the carbs and it will still work fine)

    Drain screws at bottom of bowls, two face out to each side. Keeping the carbs level, open these one at a time and drain the fuel into something. (Even a rag works!)

    LOOK at the carbs. Look them all over. Look for loose parts or parts that simply don't look right, like broken or bent parts, or lines with cracks or slits in them. Check you fuel lines and hoses too for wear or dryness. Replace if need be. Move things with your fingers and make sure things that are supposed to move DO Move freely without hanging up.

    Lay the carbs down on a bench or work space in the same direction they are on the bike, IE: #1 to the left & #4 on the right, air intakes toward you.

    I like to do the easier stuff first, so I start with the tops.
    • Remove the black caps. Watch out for the vacuum port O-rings!
    • Make sure the rubber boots are seated properly all around the lid.

    Inspect them, looking for dryness, cracks, openings, etc.
    • Check the diaphragm slides for easy movement.
    • Remove the slides & boots. Remove air needles & associated hardware.

    (Note the ORDER of these parts. What's on TOP, then next, etc, down the needle) (THIS is where that reference book comes in handy. Remember - Rule # 2 above?!)
    • Check the needles for excessive wear or bent out of straight alignment.

    (Make sure all e-clips are in the same position if you have a jet kit)
    • Look into the emulsion tubes for wear. What you are looking for is a slight EGG shape to the normally ROUND openings.

    (The emulsion tubes are what the air needles ride up & down in. They are brass and are mounted in plastic valve bodies, usually light gray, that are amounted in the carbs. They are all held in place with the main jets from the bottoms - we will get to that later.)

    If everything is fine here, clean everything and lay it aside for assembly later. Helps to keep things organized at this point! (Do NOT use solvents on the rubber parts!)

    Turn the carbs OVER. At this point, you may want to remove the air box, as you are getting into this pretty deep!!

    With the carbs turned over (you DID drain all that fuel out, didn't you?)
    • Remove the four bowls.

    (Make sure the drain screws are re-seated)
    • Check the bowl gaskets. They should be pliable, not cracked or dry.
    • Visually inspect the bottoms of the bowls and the float areas. There may be a light rust colored sediment here - don't *FREAK OUT*!! This is normal for older bikes or bikes with high mileage. As long as it's a LIGHT coating it's easily cleaned.
    • Remove the float assemblies. Take note as to HOW they remove. Are they SNUG fit? Or…did they practically fall out?

    (Almost always: Snug = good & falls out = bad)
    • Take note of the small rubber stoppers under the float assemblies. Take note as to HOW they remove. Are they SNUG fit? Or…did they practically fall out?

    (Almost always: Snug = good & falls out = bad)
    • Inspect the float needles for freedom and ease of movement. Look for clogged seats or openings. Clean with carb cleaner and blow dry off with a can of air.

    (The computer geeks love this stuff! It's only about $2 a can, and VERY HANDY!)
    • Remove the main jets. They are the large ones sticking up high in the center of each carb. They have LARGE openings, (Compared to the other orifices in carbs!)
    • Remove the pilot jets. They are seated down in the tubes where those pesky little rubber plugs came from, remember?!

    (Sometimes these stick in place, so PUSH HARD when you first start to turn)
    • Turn the carbs over and now remove the light gray plastic diaphragms.

    (I like to screw in a jet or a similar size bolt and tap them out a bit - they are seated in tight and actually held in place with the threads between the main jets and the emulsion tubes.)
    • Remove the emulsion tubes from the diaphragm bodies. Push them out.
    • Inspect all the holes in the emulsion tubes. Clean with carb cleaner and air
    • At this point, you are almost ready to clean the carbs, but not quite!!
    • Remove the air fuel mix screws. These are located on the bottom of the carbs just in front and outside of the bowls. On factory stock carbs these are protected by brass pushed in plugs. You must drill these out. (BE CAREFUL! DO NOT drill too deep as you will drill out the slot on the screw!) (Note how many turns OUT from all the way IN these are, then remove them)

    (There is a screw with a fine taper on the end, then a spring, then a metal washer, then a rubber washer.) (DO NOT dull or hit the end of the taper!!) (If you have trouble getting the washers out use a small dental pick.)
    • Remove the choke slide assembly. There are two small black plastic clips that hold it in place. Pry the open ends towards each other and then slide them back away from their seats. The choke slide then just lifts straight out!

    (Check this slide for flatness. Straighten it out so all four contact clips are lying flat on a surface and are in a straight line.)
    • Remove the choke circuit plungers. These are the pins that the four contact clips were hooked to from the slide assembly.

    (If you need to find them, simply lay the choke slide back into place!)
    • The choke plungers are held in place by two hooks on the back side of each carb. You may not need to fully remove these, and probably cannot without taking apart the four carbs, so just get them out where you can clean them and lube them.
    • Remove the fuel line(s) and their T's and their rubber boots.

    (The early Kats have 2 lines, 98+ Kats have one in the center)
    • Remove the air lines up top and their T's.

    (These are for make up air - not needed with a jet kit!)
    • NOW you can clean the exterior and interior of each carb. Plan on using a whole can of carb cleaner and a whole can of air! Make sure you clean out all ports and holes everywhere! (Get the good stuff, like 3M carb cleaner - it DOES make a difference!)
    • Clean out the small openings in the floats where the fuel sprays out. To find these, follow the tube up from small O-rings. After it bends 90 degrees it comes out in a very small brass orifice. This is a spray nozzle and MUST BE CLEAN. Spray carb cleaner in both ends of the tube until spraying it up the tube results in a fine mist coming out the nozzle. POINT the nozzle DOWN into a trash can or something!
    • Clean the pilot jets out. This is tough to do without a carb cleaning tool. If you don't have one or can't find one, (they are only about $3), then soak the pilot jets in some carb cleaner in the can's cap. Soak them over night. Once cleaned, you will be able to see a small dot of light through them. If you can't see the light, keep cleaning!
    • Once you have everything dry, reassemble it all.
    • Install new O-rings on the bottoms of the diaphragms. You can use standard plumbing # 7 O-rings, available at any hardware store, Lowes or Home Depot.
    • Install the diaphragms and emulsion tubes, then the main jets. With the new O-rings, they will be snug. Be sure to seat the emulsion tubes all the way down into the diaphragms by tightening the main jets in.

    (The emulsion tubes only fit in ONE WAY. They have a side carved off the bottom end to be able to fit properly against a small round pin down in the carbs. If you are sliding the tubes in and the diaphragms are open UP, the flat slides go to the right. The holes in the emulsion tubes will also be aligned with (3) facing straight up & down and (2) to the sides.
    • Install the pilot jets, then the rubber stopper plugs, then the floats.
    • Adjust the float heights. Most will be 14.6mm off the lip of the bowl. Do this by setting the carbs upside down and tilted so that the lips or edges of the bowls are level. Adjust by prying the small metal tab on the float needle up or down to suit.
    • Install the gaskets and then the bowls.
    • Install the Air/Fuel (A/F) screws and hardware. Be careful to assemble and install them correctly and in order. It helps to run them up into the carbs so nothing falls off. Seat them all the way in, snug, but not too tight. Then turn them out to the desired point, usually 2.5 to 2.75 turns out from dead stop. You will find that on most stock bikes, 2.5 is all you need. With jet kits more may be needed if not running OEM jets. Your stop point depends mostly on your air flow, IE: What type of air filter and exhaust are you running?

    (More fuel = more turns out!) (BE CAREFUL! turn makes a BIG difference!) (No need to replace those stupid brass plugs - they are a vane attempt by Suzuki to appease the EPA!)
    • Turn the carbs over.
    • Lube the choke plungers with a little bit of WD-40 on each rod. Re-seat them all, then pull them out and let the springs suck them in a few times to make sure they work properly!

    (You can also put a drop in the port hole up inside the top of each carb and then pull the plunger out a ways to let it run in!)
    • Install the needles & their hardware in the center hole in the air slides, then install the air slides into the diaphragms.

    (Remember that reference book - Rule # 2? Now would be a good time to look at it!) (Make sure the rubber boots are seated all the way around in the lip of each carb.)
    • Install the O-rings for the vacuum ports. (Early Kats only)
    • Install the caps. Make sure the rubber caps for the vacuum ports are OK. They should not be dry or cracked or split and they should have clamps.
    • Check the air slides to make sure they move freely, make the same “sucking” sound, like they're drawing a vacuum, and to make sure they return to their seated position easily.
    • Make sure the throttle bodies move easily and the springs allow for quick return. If you pry them open and let them go you should here a thud or sharp stop.
    • Reinstall the idle adjuster cable until it just barely touches the starter tab of the carbs. Now look into the engine side of the carbs at the butterfly valves. (There are three small holes - familiarize yourself with them.) Look at carb # 3 and adjust the idle cable until the first small hole (towards the outside of the carbs) on the bottom of the carbs is HALF VISIBLE. Then adjust carb # 4 using its idle adjustment screw, (located from the top between the carbs - it's on the arm that moves when you twist the throttle). Take this carb to the same point by only adjusting the screw. DO NOT adjust the cable any more - it is only for carb # 3 at this point. Next, adjust carb # 1 to WHATEVER carb # 2 is, so they are equal. Then, adjust carb # 2 to the same point as 3 & 4 (first hole half open). Once all four carbs are equal and at the same point, (HALF the first small hole showing open) you have visually synchronized your carbs! You are now ready to reinstall them in the bike and synchronize them exactly.
    • Install the air box onto the carbs FIRST!! The clamps face down so that the screw heads can be reached from the bottom and the outside, 2 each, IE: 1 & 2 face left, 3 & 4 face right. You can also remove the air filter to PUSH the rubber seats on over the carbs by sticking your hand inside the air box to assist. Once you have the air box fully seated with all fours clamps back on the carbs then reinstall the filter.
    • Reinstall the throttle cable(s) while the carbs are still off the bike.

    (MUCH easier!)
    • Reinstall the carbs. Make darn sure that the clamps at the engine intakes are very loose and are up top! PUSH (HARD) on only the carbs themselves to seat them back into the engine. Crank down the clamps being careful to make sure the screws are at the top.
    • Reinstall the choke cable, and fuel line(s), and air lines and the main exhaust blow off hose from the top of the engine to the air box.
    • At this point, I'd suggest changing the plugs, then using a temporary bottle give the beast some gas! Don't forget to plug the vacuum line coming from the left side of carb # 4 while you run the bike.
    • Once the bike is warmed up, adjust the idle, and then shut it off to hook up your synchronization tool, then synch the carbs.

    Originally written by KWBender AT gmail DOTcom

    See also

    Carburetor Settings and Specifications

    Carb Parts List

    Carbs 102 98+ Bikes
    Attached Files
    Last edited by Kreylyn; 06-23-2019, 10:02 AM. Reason: Updates

    • Kreylyn
      Kreylyn commented
      Editing a comment
      Needs further edited and updated with current information, checked details for steps. Fix broken links. Format changes.
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