Next up is the carbs. This job will prove to be the most difficult and is also the MOST IMPORTANT job to get done properly if the engine is to run reliably and run well. Do it right the first time or be prepared to do it again and again and again. Even when done properly you will likely find yourself removing and replacing the carbs a few times before the engine will run properly. These carbs are old school and must be handled with care. Some of the parts for these carbs can be difficult to find and can be costly once found.


To clean the carbs you will need a good quality carb cleaner. A litre will be enough if you’re not wasteful but you might see that smaller quantities are more costly then one gallon cans. You’ll also need some spray-able carb cleaner, penetrating oil, a compressed air source, an assortment of tiny bottle brushes, 4 suitable sized containers for small parts, 4 zip lock bags, a container big enough to soak a carb body in, a small hammer, a small punch, safety glasses and an assortment of different sized shot head screw drivers. A heat gun would also be handy.  Large coffee cans work real well as soaking cans and disposable food storage containers work well for small parts. The tiny bottle type brushes can be found in spray paint equipment cleaning kits. If you prefer to rebuild the carbs one at a time without removing them from the mounting bracket you will need a gallon of carb cleaner and a container big enough to place the carbs into while they remain on the bracket.

Check your manual for the procedure to remove the carbs from the engine and remove them. Place the bank of carbs on your CLEAN & CLUTTER FREE work bench. If the carbs are very dirty give the outside of them the once over with spray carb cleaner so the work bench will remain somewhat clean when you start taking the carbs apart. Label the carb positions with a black magic marker on the back side of the “L” bracket that the carbs are mounted to and on the back side of the carbs so they can be returned to their original locations. Also make reference marks on the bracket and one of the carbs so it is positioned properly on the rebuild. You can also scratch the numbers into the bracket and backside of the carbs if you like. Check the carbs over closely to become a little bit familiar with what they look like. Take photos if a camera if available. Pay attention to the chock rod position and set up. Check the locations of the hoses and the way they are routed.  Check out the way the return springs are interlocked with each other between the carbs.


I will start with the removal of the carbs from the mounting bracket but if your intension is to not dismount them you can just skip this part.  The first thing to do is remove the idle adjustment knob and spring that is mounted in the middle of the bank of carbs. Next up is to remove the chock level and chock rod. KEEP YOUR EYES OPEN FOR SMALL PARTS including the tiny ball bearings and their springs. They control the chock rods movement and position. They are in the carb bodies so they tend to “pop” out as the rod is slid out past them.




There is a spring under the chock lever itself as well as a small “E” clip and a few small washers. To remove the lever remove the “E” clip at the level end of the rod so the lever guide can come off the end of the rod. Remove the “E” clip from the small shaft that holds the lever into it bracket. Remove that shaft and the lever will come off the end of the rod. At each of the carbs you will notice a fork that is held to the rod with small set screws that have slot heads on them. Using a PERFECT fitting slot head screw driver loosen the set screws. The slots will STRIP EASILY if the slot on the screw driver is not a perfect fit so use care. Once the set screws are loosened off the rod can be slid out of its position toward the lever side of the carbs. This is when you need to be careful not to loose those tiny ball bearings and springs. Put the lever and rod parts aside in a safe place.

Next is the removal of the carbs themselves from the mounting bracket. The large Philips

head screws that hold the carbs onto the mounting bracket WILL BE VERY TIGHT. The best way to get them out without stripping the screw heads is to use screw driver bits from a socket set that are a perfect fit along with a small ¼ drive ratchet. If you strip the screw heads you will have to remove the screws with vice grips and replace the screws. Use some anti-seize on these threads during the rebuild even if the screws are replaced. After you get the mounting bracket removed you can loosen all the Philips head screws on the top of the carbs. These alloy screws may also be rather tight and can have the heads strip out easily. So again, use a socket set type bit with a ¼ inch drive ratchet. Once these screws are loosened you can remove the bridging plates from between the carbs ONE AT A TIME by removing the screws that hold each one in place and then replace the screws after the plate is removed. You do not want the tops coming off the carbs just yet. Put each complete carb into a container as they are removed from the set. OK, now you have 4 individual carbs and can rebuild each one, one at a time without mixing up the parts from one carb to the other. 

The strip down process is the same for each of each carbs involved.  The insides are all the same but the carb bodies are different depending on the carbs position when mounted to the bracket. Now you know why you numbered them.  Start by giving all the visible jets a shot of penetrating oil. Most if not all of the jets will be brass and THEY WILL BE TIGHT. Make sure that you use screw drivers that fit the slots in the jet perfectly. Otherwise they will get striped and requirement replacement. While removing the jet care must be taken to not damage them in any fashion that would alter the size of or partly block the holes of the jets. Doing so would have the same effect as putting in different size jets.

On what was the air box side of the carb remove the air jet that is at the 8 O’clock position. Put it in one of the 4 containers you have and label the container for the carb you’re working on. There’s nothing to remove from the holes in the 4 or 10 O’clock positions but those are galleries that will need to be cleaned. There is nothing to remove from the engine side of the carb but you must confirm that the butterfly valves move freely with no binding in their range of travel. Do not remove the butterfly valves unless it becomes necessary to change the butterfly valve shaft seals.

Now it’s time to remove the carb tops. Under each one you will find a spring and a metal slide that is suspended from the carbs top edge on a flexible rubber diaphragm. The rubber diaphragm may have a small amount of gasket sealant under its lip so care must be used to lift the diaphragm off the top of the carb. The diaphragm must not be damaged so don’t use anything sharp to free it. It is easiest to remove the diaphragm and slide by reaching into the mouth of the carb with your fingers and push the metal slid upward to the end of its travel. Once in the upper most position you should be able to grasp the rubber diaphragm and break the bond at the top of the carb by working your way around the diaphragm with your fingers. Once the diaphragm is fully free of the top of the carb lift it and the metal slide with the needle jet attached straight out of the top of the carb. Put this assembly in a zip lock bag and seal the top so the diaphragm will not dry out and shrink too much.  Label the bag as to the carb it came from.

Now flip the carb body over and remove the float bowl. There are 4 screws per bowl and they WILL BE VERY TIGHT so approach them as you did to loosen the carb top screws. Once the float bowl screws have been loosened about half way, break the bond between the carb bowl and the carb body.  Breaking the bond between them now while the bowls movement is controlled by the screws will prevent damage to the floats if the bowls bond should break suddenly. If the bond seems reluctant to break you can tap on the bowl with a small wooden of plastic mallet. You can also pry with care at a few locations around the perimeter of the bowl but that will not be likely be necessary. The bowls tend to be well bonded to the gasket but “pop” off all at once as soon as the bond is broken. In any case try not to damage the gaskets unless you are planning to replace them as part of the carb cleaning / rebuilding process. Once the float bowl is loose, finish removing the bowl screws and lift the float bowl straight up off the carb body. Now remove the bowl gaskets and try not to tear them.  They also tend to be well bonded to the bowl or the carb body but usually pop off all at once just like the bowls did. If they don’t and any gasket material is left on ether surface, you will need to clean the gasket surface during the cleaning process.  

Once the bowl is removed you will in almost all cases for the 78 and 79 models be looking at a brass float. That float is held to the carb body on a shaft or pin that is pressed into the two towers that support the pin and float. The pin will have a flat nail type head on one side. The pin comes out of the towers from that side. GREAT CARE MUST BE USED TO NOT BREAK THE SUPPORT TOWERS.  Start by spraying the pin where it meets the towers with penetrating oil. If there are NO GAS OR CARB CLEANER FUMES PRERSENT the heat gun will be handy to use. DO NOT USE PROPANE OR PAPANE TOURCHS. YOU WILL MELT THE ALLOY PARTS BEFORE YOU RELIZE WHAT YOU HAVE DONE. The carb’s body will heat up faster then the steel pin so heat can help make the bond between the two weaker.  The pins can be tapped out  with great care using a small punch and a very small and light hammer like a jeweller’s hammer. If you heat the towers up with a heat gun they will likely come out pretty easy with the small punch.  Once the pin starts moving you may be able to get a hold of it at the head end and pull it out with a twisting motion that turns the pin in its bore. You can also buy carb pin presses to remove the pin if you’re concerned about damaging the towers. It really depends on your skill level with hand tools. However, penetrating oil, heat and tapping with care  will get the pin out safely. Once the pin is removed lift the float straight up out of the carb and put it in your container that is labelled as being for this carb.  For some the pins can be removed with care using cut cut type plyers. When side cut type plyers are used get the jaws under the head of the pin and use the base of the tower to pry the pin out with geat care. Some also have good results with needle nose plyers as are seen being used in the photo.



With the float removed you will see the float needle valve. Remove the needle and the seat. You can also see the main jet. It is right in the middle of the carb body within the bowls space. Remove it.  There is a brass screw on the top of a single tower. That screw covers the pilot jet which is down inside that tower. Remove that screw and the pilot jet that is inside that tower. You will need a small screw driver to get down into that tower to remove the pilot jet. I use a “tuners” screw driver which is different from the usual flat head screw driver in that there is no flair at the tip where the slot is made at the end of the shaft. While the carb is in this upside down position use a small wood dowel to tap out the emulsion tube. It is directly under the main jet. In fact the main jet was threaded into the bottom of the emulsion tube. The emulsion tube will come out the top of the carb once it is tapped out. If the emulsion tube is seazed in place DO NOT ATTEMPT TO TWIST IT OUT. There is a locating pin on it and twisting will damage the setup. So if seazed in place heat up the carb with the heat gun and then cool it off with sprayable penatrating oil. Heat it up again and spray it down again. Let it sit for a few hours and tap it out with a wood dowel If it remains seazed in place repeat the process untill it can be tapped out.

Now you need to remove the pilot screw. It is under a protective plastic cap on the top of the carb on what was the engine side of the carb.  Remove the plastic cap and carefully turn out the pilot screw. When it is out the screw should be very sharp like a needle at its point. If it is blunt or broken at its point you will need to replace the screw. You will also have to make sure that the missing tip is not jammed in place at the bottom of the hole that the jet came out of. If it is you will need to remove it without damaging the sides of the hole. If you damage the sides of that hole the screw will not offer fine adjustments as it is intended to. Carefully remove the chock circuit parts for cleaning. You might want to put these parts in their own small container as they came out of the carb body and clean them as a secondary job. Put all these removed jets, floats and the float bowls into the container that you have for this carb.

That’s it for stripping the carb bodies of the jets and parts that need to be checked and cleaned so now it’s time to soak the carb body in carb cleaner. You will need to soak the carb body in two positions because YOU MUST NOT ALLOW THE BUTTERFLY SHAFT OR ITS SEALS TO BE SOAKED IN CARB CLEANER. If you do the seals will be damaged and you will have to replace them.  They can be found easy enough but are not cheap and require that the butterfly valves be removed. You should therefore put the carb body into the container you have chosen for soaking the carbs in with the end that normally faces the engine in the down position. The carb will be sideways in the container. Now add the carb cleaner to a level that is just below the butterfly valve shaft. Let the carb soak as per the instruction on the product. When that soaking time frame ends remove the carb body and turn it over in the container. The carb is still sideways in the container but the butterfly shaft is towards the top. Add more carb cleaner to a level that is just below the butterfly valve shaft. Soak as per the products instructions.  Once the carb has been soaked in both positions without the butterfly shaft being soaked you can remove the carb and start the cleaning process. Use your small brushes to clean every hole in the carb body. Some will be galleries other will be castings but do them all in any case. Push the brushes into all the holes / galleries with a twisting motion as you would if you were cleaning a baby bottle. Do this several times for each hole / gallery. Spray carb cleaner into the galleries from time to time as you do this job. After the brushing is done it would not hurt to soak the carbs again but do so without soaking those butterfly shaft seals. Adjust the level of the carb cleaner in your container accordingly when the shaft seals will be at the lower level as was the case when you started the soaking cycle.  After the re-soak clean with the brushes again followed by use of spray carb cleaner followed by compressed air. WEAR SAFTY GLASSES FOR THIS AS MANY OF THE GALLERIES WILL HAVE THEIR EXIT POINTS FACING YOU  OR WILL BE DEAD ENDS AND CARB CLEANER IN THE EYES IS NOT NICE. Sprayed carb cleaner and compressed air should flow freely through all the galleries and enter at one point and exit at another. The spray or air will travel through the galleries and exit through the jet holes where the jets came from when you stripped the carbs. The insides and outsides of the carb bodies should also be cleaned with soft brushes to remove any and all fuel gum and deposits. Before you consider the carb bodies cleaned be sure you have done a complete job. If you don’t and you have carb related problems you will be second guessing your original work and doing it again. Repeat this process for each carb without mixing up the parts.

Now that the carb bodies are clean the balance of the parts there were striped off each carb can be cleaned. These parts also MUST be spotless and inspected closely. All the jets must be clean inside and out with no fuel gum or varnish left on their surfaces. The emulsion tubes will likely require the most work. If they are heavily gummed up you may want to clean them with a VERY SOFT brass wheel that will clean them but not alter their surfaces. All the holes through the sides of the emulsion tubes must be clean. Hold them up to a light source to confirm that you can see through the holes all round.  Run one of your small brushes through the hollow center and make sure this tube is CLEAN. Clean the float bowls of any fuel varnish / gum and also clean the fuel delivery tube hole. There is a tiny pressed in jet in that hole that is not to be damaged but must allow for fuel flow. When carb cleaner is sprayed into the hole at the bottom of the float bowl the fluid will spray out of the hole on the bowls edge. Spray the cleaner both ways to make sure this gallery is clean. Again, wear safety glasses so you don’t get carb cleaner in your eyes.

The floats them selves MUST be handled with care. They can easily be dented or damaged. The floats can be cleaned with a very soft brush. Once they are clean you will want to test them for leaks. You can do this by submersing each one into a container of BOILING HOT water and see is any air bubbles appear on the float at any leak points. If the floats are good dry them with compressed air and inspect each one closely to confirm that the floats themselves are at 90 degrees to the arm or tang they are soldered onto and that the tang in flat. If any adjustment is required do so with GREAT CARE and make the adjustments a little bit at a time.  

Clean and inspect the float needles and seats very closely. It does not take much to damage the machined surface and they MUST close fully or fuel flow will not be stopped even when the valve is closed by the floats. The little spring loaded nipple on the top of the valve must work smoothly and do so through its full range of movement.  Clean the chock circuit parts with care and do make note of how these parts go together. Again, use soft brushes on the machined surfaces.



Once all these parts are cleaned and inspected as being good the rebuilding of the carbs can be started. That being said I can not stress strongly enough THAT YOU MUST BE COMPLETELY CONFEDENT THAT THE CARB BODIES, ALL THE JETS, FLOATS, ETC. ARE PERFECTLY CLEAN AND UNDAMAGED. These old school carbs will not work properly if even the smallest missed bit of fuel gum or grit finds its way into a jet or blocks one of the tiny galleries in the carb body.  Pay close attention to the fuel and vent “T”s as well. They tend to get messed up and may leak if they are no longer a tight fit in their bores. They can be replaced but they are hard to find and are VERY costly. Sometime an O-ring for fuel injection systems of just the right diameter can be placed between the 2 ridges of the “T”s seal to create a good seal between the “T”s and the bore walls. In any case, FUEL MUST NOT BE ALLOWED TO LEAK FROM THE “T”s OR FOR THAT MATTER FROM ANY PART OF THE CARBS. FIRE WILL ENSUE IF YOU ALLOW THE CARBS TO BECOME LEAKY.  If you’re wondering why we have not cleaned and inspected the diaphragms and upper carb parts yet that is because we want to handle these parts minimally to avoid damaging the diaphragms or letting them dry out and shrink. These parts will be cleaned, inspected and installed one carb at a time as the last step in the rebuilding process.

            Now it’s time to rebuild the carbs. Start this job only when you are completely sure that you have cleaned all the parts to a like new condition.  Any questionable parts should be replaced and replaced.

            Start by applying the slightest amount of light oil to the rebuilt chock plungers. Insert them into the carb body they came from and tighten the brass holding screw into the carb body.  Don’t use a lot of force on these nuts. Just firm them up. When all the chock plungers are reinstalled into the bodies mount the bodies start mounting the carbs back onto the mounting bracket. Working from one end to the other install each body onto the bracket and install the fuel and vent “T”s between the carbs as you go. Make sure the butterfly valves are interlocked together properly between the carbs. Do not tighten up the mounting screws just yet when you’re mounting the bodies.  You may also want to install the fuel and vent hoses onto the “T”s before you install the “T”s because it’s a tight fit to get the hoses on after the carbs are mounted.  Don’t forget the spring clips that hold the hoses onto the “T”s. With the carbs mounted TEST the operation of the butterfly valves. All should move together. Confirm that the spring loaded adjusting screws are positioned properly for the adjustments that you will be making for the tune up.

Once all the carb bodies are back onto the bracket it’s time to install the chock forks, locating balls and springs and the chock rod itself. The carb bodies should not be tightened to the bracket at this point so that the rod can be installed. Make sure the rod is straight or it will bind. OK, start by applying a slight amount of light oil on the rod so it will slide into place easier. Feed the rod through the rod holes and place the choke forks and locating balls with springs as you feed the rod through the carb bodies. Make sure the chock forks are facing the right way and are properly engaged with the chock plungers. Once the rod is in place firm up the rod holding set screws but not too tight.  You will see a predrilled hole where each set screw will contact the rod. With the rod held in place TEST its operation.  It should move sideways smoothly and move all of the chock plungers at the same time and for the same distance. If this checks out you can tighten up the set screws. Leave the chock level off for now. If you install the chock level at this time, the carbs will not sit flat on the bench when you’re working on the float bowls parts. Tighten up the bracket screws now (did you remember to use anti seize grease on the screws?) and then retest the chock rods operation. If all is working as it should, you can flip the carbs over onto their tops and start installing the jets.  Install the jets that go into the air box side of the carb mouths. Do not over tighten the jets. They need only be firm. Use care to not distort the jets when installing them.  Next is to lay the barbs on their side with the tops facing you so you can reinstall the emulsion tubes. Look at the emulsion tubes closely and you will see a pin on them that must line up with a slot in the emulsion tube cavity of the carb body. Install the emulsion tubes. With them in place you will not need to install the main jets with their washers. Remember, the main jets thread into the bottoms of the emulsion tubes and will hold them in place. Now that the emulsion tubes will not fall out you can flip the carbs over so the carbs on resting on their tops. Install the pilot jets down into the towers in the carb bowls and install the cap screw into the top of the towers.  Now it’s time to install needle valves and the floats. Install the needle valves into their seats followed by the installation of the floats.  The floats cans go into the carb so what you’re looking at the flat surface of the floats. Slide the float pins into place and then carefully tap them into place.

Now you will want to set the floats for proper float height. The spec measurement for float height is taken from the gasket surface to the top of the float WITHOUT THE GASKETS IN PLACE.  



Bend the tang in the middle of each float ever do slightly for each adjustment you make until the floats in all the carbs are to the same spec. Try to bend these tangs squarely as compared to twisting them. When you make an adjustment to the float tang give the float a little push down and let it spring back to its static position and measure again. Repeat until each pair of floats in each carb is correct. When all the carb floats are correct check the float stop (it’s the little tang at the side of each float arm that is bent so that it contacts the float tower and restricts float movement. It’s job is to make sure the needle valves can not fall out of place when the carb bowls are empty. To confirm that the float can not drop so far that the needle can fall from its seat turn the carbs over to their normal installed position.  The floats will drop to their max low position but the needle valves must not fall out or come out of the seat so much that they can get off center and bind when the floats go up.  Test then for proper operation. If they work properly you can put the gaskets back in place. The gaskets are a little funky looking but only go into place one way. When installed properly there will be what looks like a half of a hole in the gasket showing on the bracket side of the carb bowls gasket surface. It looks like perhaps the gasket is not placed correctly but this is normal.  Apply some anti seize to the threads of the bowl screws and install them.  DO NOT OVER TIGHTEN. Firm is all that is needed. Install the bowl plugs with their copper gaskets. Be extra careful on these plugs as you need to get a good seal but not strip the threads in the bowl. If they leak you will know when you do the fuel level test that follows.  If they leak, replace the copper gaskets or heat them up good and hot and then douse them in cold water. If they are not smooth on their faces you can run them over some 220 wetted wet / dry sand paper with the gasket on the tip of your finger to smooth out the faces.  

                 Now you can test the needle valves to confirm that they do in fact stop the flow of fuel when the bowls fill. THIS TEST MUST BE CARRIED OUT WITH GOOD VENTALATION, NO SPARK OR FLAME PRESENT AND WITH CARE. IF YOU’RE CARELESS, SOONER OR LATER, A FIRE WILL ENSUE. Support the carbs in a fashion that will have them LEVEL front to back, side to side and in the upright position as they would be when installed. I set them up in a vice with the jaws set to just catch the flange of the bowls. They just rest in the jaws without the jaws tightened. Position all the hoses upward. Using a small funnel that will fit into the fuel hose (Dollar store jobbies) and doing one pair of carbs at a time, add fuel until fuel is to the top of the hose. You don’t need to fill the funnel. If the needle valves are working no fuel will flow from ether mouth of the carbs and the fuel level in the hose will not drop. If fuel is flowing past the needle valves give each bowl a tap to confirm that the floats have not become fowled by contacting the sides of the carb bowls. If tapping the bowls stops the flow of fuel you’re good to go. Repeat this test for the other pair of carbs. If fuel flows on ether pair even after tapping on the bowls during the test, you will have to check the needle valves again or replace them out right.  If you want to inspect them you will need a magnifying glass to check the machined valve tips for scratches / damage.                 

             For those who want to go the extra mile on float setup you can check the actual fuel level in the bowls regardless of float height. This test can only be carried out after the needle valves are confirmed to be working. To the test you will need to remove one of the bowl drain plugs and take it to a specialty shop that sells brass fitting including metric threaded fittings. Buy a threaded hose nipple that can replace the bowl drain plug. Make sure the threads are a perfect match. I would buy 4 of these fittings so all 4 carbs can be checked in one operation. However, 1 will do. Install these nipples into the bottom of the carb bowls where the drain plugs usually go and attach a 1 foot length of CLEAR fuel hose to each nipple. Loop the hoses in a fashion that has the top open end of the hoses well above the bowl where the bowl meets the carb body.  Make sure the hoses are not kinked. With the carbs leveled as per the needle valve test, fill the carb bowls again. You will see the fuel travel up the clear hoses until the needle valves close. The fuel level in the hoses will be the same as the fuel level in the bowl for each carb. The fuel level in all 4 hoses should be the same and the level should be right in line with the washer that is between the bowl screws and the bowl shoulders where those screws go.

So now it’s time to check out the slides, slide needles and diaphragms.  I will tell you now to make sure the slides go back into the carb they came from in case you forgot that all the parts from each carb should go back into the carb they came from. First off check the diaphragm to make sure there are no tears in it. If there are no tears start by cleaning the diaphragm with a rubber restoring product. Don’t use those common rubber / vinyl products that make rubber shinny (you know the ones I mean). Go to an auto supply shop and get a good safe product for this job. If those diaphragms are not soft and flexible the carbs will not respond as they should. If cash flow is not an issue, I would replace them out right with new ones that can be found at a few sources. Next is to remove the needle to confirm that it is jetted properly. To remove the needle you will need a pair of LONG nosed circlip removers for removing internal circlips.  While holding the SPRING loaded needle remove the internal circlip that is down at the bottom and inside each slide. Don’t let go of the needle or the small parts will be sprung out of the slide and potentially lost. Put your hand over the opening at the top of the slide and let the needle go. If it does not pop up into the slide give it a little help and it will let go. Inside the slide you will now have the plastic needle holder, the needle with a plastic ring, a tiny washer, a tiny circlip and a spring on it.

Clean all these parts in your carb cleaner but DO NOT SOAK THE SLIDE BODY. Clean it with a SOFT rag that is dampened with carb cleaner. DO NOT GET CARB CLEANER ON THE DIAPHRAMS!!   If by chance the slide is real gummed up you can soak it standing upright in carb cleaner with the diaphragm in its usual cupper shape so it’s above the carb cleaner. Once all these parts are clean confirm that the tiny circlip on the needle is in the middle position on the needle.  There are 5 possible positions so you want # 3 from the top or the bottom.  

Before you start rebuilding the slide look closely at the holes in the bottom of the slide. You will see that the ones at the sides are OFF center. The locating pins on the bottom side of the plastic needle retainer are also OFF center so it only goes in one way. Put the tiny washer under the tiny circlip followed by the spring. Under meaning feed them onto the needle from the pointed end. The small plastic spacer goes above the circlip on the needle.  Put this into the bottom of the slide. With the needle protruding out the bottom of the slide you can now grab it and pull it until it bottoms out in the slide. Don’t let go of the needle as it will be spring loaded again. Now put the needle retainer into place so those OFF center locating pins fit into the OFF center holes at the bottom of the slide. It will only go one way and you will know when it is fully seated because it will be a snug fit and it will reveal the circlip notch above its shoulder. Put the circlip into place and make sure it is fully seated. I like to place it and then push down on the exposed edges of the clip with a small flat head screw driver. It will pop into full seated position if it was not properly aligned. Now you can let go of the needle. It should stay in place but move around  little with finger pressure. It’s spring loaded and sort of floats in it seated position.  

Now the slide can be placed into the carb body. The needle will go through the hole that is centered below the slide’s bore. That needle actually goes into the opening of the main jet which is mounted in the carb bowl from the bottom side. If you look at the edge of the diaphragm you will see a tab. That tap must fit into the same shaped relief on the top lip of the carb body.

Line the diaphragm up so it is ready to go. Now THIS IS IMPORTANT, apply a little bit of Yamaha bond to the grove where the diaphragm’s edge goes. The diaphragm MUST be air tight and from the factory a sealant IS used at this location. With the bond in place feed the lip of the diaphragm into the groove This can be a tricky job but MUST be done properly or the diaphragm can get damaged or not seal properly It WILL be a slightly stretched fit and will want to pop out of the grove before you can get the carb top on so WORK FAST. The Yamaha bond will however, make this easier. Have the carb top clean and ready along with the diaphragm spring. Once the diaphragm is seated drop the spring into the slid and put the carb top on. Make sure the spring is seated over the carb tops locating casting at the middle of the carb top’s underside. Secure the carb top with of the carb top screws place kitty corner and not fully tightened. Do each carb the same way until all are topped and ready for to mount the brackets that go between each one. These are the mounting plates that go from top to top across the carb tops. Without letting the tops come off the carbs, which might allow the diaphragms to pop out of position, install the plates.  Do one at a time and you can now firm up the carb top screws as you get the plates in place. Make sure the center plate is mounted properly to hold the idle adjusting screw so it is at the back side of the carbs which is on the wider mouthed side.

With all the plates in place you can now bench test the operation of the slides. Reach into each carb with you fingers from the large mount side and push the slide upward. It MUST move up smoothly and fully. It MUST also pop back into its original position as soon as it is let go. Do this a few times to confirm that each carb slide is working properly. If that’s good you can now confirm that the slides will stay up when their air port is blocked. Do this by pushing the slide upward and while holding it in the up position block the elongated opening that is on the large mouth side right at the 12 O’clock position. You can block it with your finger. With that opening blocked the slide should stay in the up position or slide down very slowly when you let the slide go.  If any of these tests fail, you will have to open up the carb in question and check it out closely for the cause of the problem. If all is good, you can install the idle adjusting screw and spring. The spring goes on the adjusting knob’s shaft after it is through the top plate.

That’s it for carbs other then tuning them which is a completely different story. If you have properly cleaned and rebuilt them they will work well and the bikes engine will run strong. If there are any issues with leaking / flooding, the float needles and seats might need replacing.



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  1. Kurt Hertel says:

    Very nice articles. I have a 79 XS1100SF I purchased new in 79. I let it sit in storage for 11 years and am now trying to get it ready for sale. I needed to repair a broken (rubbed through on the timing plate) wire for the pick up coils and didn’t realize until after I unmounted them that my Hayne’s manual does not list the air gap spec. Could you give me this spec from your technical information? I also removed and replaced my RC Engineering 1220cc piston and liner big bore set. 10.5:1 compression and a set of 36m/m Lectron carbs with the 1100 rack. I also replaced the WEB cams I had installed years ago. I am interested in selling all of those high performance items. Another project perhaps??? I enjoyed your news letter and all your hard work and attention to detail. I hope you can help me with the spec. Thanks,
    Kurt Hertel
    Rochester, NY

    • If you are refering to the gap between the pick up coils and the Governor’s fin tip this is what you want.
      Now before the timing plate goes on you will want to check the gap between the governor’s fin tip and the surface of the pick up coils. The gap beteen the tip of the governor’s fin and the pick up coil is .07 mm. If you look closely at the face of the pick up coils that faces the gonernor you will see a raised line on them. The measurement is taken between the governor’s fin tip and the pick up coil when the fins tip is right at that raised line on the pick up coil. This measurement must be very percise if the coils are going to fire on time as expected.


  2. Bro says:

    Best place to purchase XS1100 floats?

    • When ever possible I try to find OEM new old stock carb parts. If that fails I have had good results with S.C.I. on ebay. Note that if you go from brass to plastic or the other way you will likely have to confirm the fuel height in the bowls manually.

  3. kurt beier says:

    Hi, I recently purchased a 1980 XS 1100 with only 9K original miles from the original owner. The bike is completely original and in mint almost museum condition. The original owner had it setting for a long time and took it to a shop and had the carbs gone through. When he got it back it did not run like it used to. He kept taking it back and the guy kept charging him but still the bike would not run smooth. Guess he got tired of dealing with it and decided to sell it to me. It starts easily when cold with the choke full open (has two positions) but had a big flat spot between idle and 3K rpm after warmed up and choke turned off. I figured it was a carb problem since it runs smooth when cold and choke on. I got a manual and started checking things out. Who ever worked on it ended up making a big mess of all the fuel lines (1980s had the vacuum delivery system and negative pressure carbs) and vacuum lines having every thing going to incorrect locations. I think he was attempting to compensate for whatever the problem was. I have straightened out the fuel lines and vacuum lines putting them to how they came stock. I checked out the vacuum fuel delivery system and that appears to be working ( allows fuel to flow when vacuum applied). The bike still starts easy and runs smooth with the carb pulled to full on, but will not stay running when the choke is in middle position or taken off (acts like there is no fuel) and Just immediately cuts out. I pulled apart the carbs and evey thing is perfectly clean inside. Any ideas on what the problem could be? I am sure there is an easy solution and that the guy who was working on it just has something else out of wack that I do not know about. Blessings. Kurt B in CA.

    • If it will run with the chock on I am lead to believe that the engine is being starved for fuel. Unless the carbs are simply not adjusted properly, I would suggest that you completely disassemble them. When I say completely I mean COMPLETELY. On these old bikes the carbs MUST be in pristine condition for the engine to run as intended.
      I would put all the jets and bodies through an ultrasonic cleaner if you can access one or take the parts to a place that can do it for you. If not, soak all the parts and bodies in a high quality carb cleaner. One carb at a time to avoid mixing up the parts. After soaking for the recommended time frame run brushes through all the openings in the bodies. You can use spray paint gun cleaning brushes. Their pretty small so they will fit into most openings. Brush and spray carb cleaner through all the opening. Wear safety glasses and be careful. In a few cases the exit points of the galleries will be pointing right at you. Use compressed air to complete the job after you’re sure that all the galleries in the bodies are clean. Blow them all out which also dries them at the same time. Assemble with care and check every jet as you do this. Confirm that all the jets are correct for your carbs and year of bike or more so, year of engine based on the year of bike it came from if not orginal.
      On the bench make sure all the moving parts on each carb work as they should. All moving parts must move smoothly and consistently EVERY time. Once that’s confirmed rack them and test again for smooth and consistent operation of all four as a connected group. Bench test them to confirm that they hold fuel and that they do not over flow. The needle valves must be working perfectly for these carbs to function. USE HIGH TEST FUEL because it does not have any ethanol in it. Not up here anyway. Ethanol is problematic for these old carbs. Once the carbs are prestine clean, reinstalled them on the engine and tune them up as per the manual.

      • Rick says:

        Hj.i have rebuilt the float and bottom of the mikuni carbs on my 1979 sx1100.the floats appear to be working well.but when i put fuel to the carb fuel squirts out of the throat.i cant figure out what is causing that?it seems to b bypassing the float? Is their a solution to my problem.ty.

      • If fuel is getting past the bowls and into the throat of the carb you have one or more issues taking place. First thing to check is the seal of the float needle valves. If the needle valves do not seal 100%, fuel will continue to flow until the bowls overflow into the carb throat. If the needle valves are working as they should and seal 100% than you need to check the float height. The floats must be set at the proper height or they will not close the needle valves when they should and fuel will continue to flow into the bowls until the bowls overflow into the carb throat. Some simpler things to check include making sure the fuel is going into the carbs by way of the fuel hoses and not the vent hoses. Make sure the vent hoses are not blocked.

  4. Tim Mashewske says:


    I am in the process of rebuilding a 1979 xs1100 special and I have everything done. I start the bike and it seems to Idle just over 1000 rpms then after about ten minutes of running, the rpms sky rocket to 6000. I have had the carbs off a number of times and everytime no matter what I do, the same problem occurs. when I pull the choke to see if it will flood out, nope just bogs down a bit and keeps running. There are brand new carb boots on so if it is getting air from some where, I am at a loss as to where. Any help would be great.


    • Spray some quick start around the carb bodies before the engine is so hot that a fire might ensue and see if the revs go up. Possible leak locations include the butterfly seals at the ends of the butterfly shafts, the auto advance hose on carb #2 that MUST ONLY go to the auto advance device, the nipple covers on the mounting boots on the engine side, the air box boots on the air box side (they sometime get folded over during installation). The carbs may also just need to be synced if that’s not done yet. It goes without saying that something is changing when heat has its effect.

  5. Nick says:

    I found out one reason why the carbs are leaking is: the floats falling down too far !!! There is a tong on the float that can be adjusted to stop the float from going down too far. The reason for the leak is that the float will push against the needle side ways and the needle will NOT go up to close the fuel passage. 1 or 2 mm. of needle opening is enough for fuel supply.

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