RES
ArboristSite Operative
I recently rebuilt two carburetors, a Tillotsen and a Bing. Here are the steps I took. I do not claim to be an expert here so if you have any better suggestions please feel free to chime in.
• I usually clean off as much dirt and grime from the outside of the carburetor especially around the springs before I take it apart. I block both the inlet and the outlet with small pieces of crumpled paper towel and spray it with carburetor cleaner using the red plastic spray tube. I then blow it clean with compressed air.
• Make sure you have a selection of small screwdrivers in good shape. Since there are still a lot of slotted screws used, make sure your slotted screwdrivers have shape edges and fill the slot of the screws. File or grind if necessary making sure the screwdrivers are clean when you are done. If you ever see a watch maker he has a large set of small screwdrivers with a stone to keep them dressed.
• I have a magnetic tray to hold the small metal parts and screws. I use a section of the tray for each section of the carburetor I take apart.
• Start with the H and L adjustment screws. Turn them in until they gently bottom out. Count the number of half turns and mark it down. This makes it easier to start the saw when the carburetor is put back on. Bag and tag each screw with its spring. On some carbs both H and L are identical. I am not sure it matters if you mix them up. But to be on the save side, I put them back the way they came out.
• There is no reason to mess with the Large Stop screw. Just clean around the spring thoroughly with your carb spray.
• Remove the pump cover. Make a sketch of the cover orientation. As you remove the gaskets and diaphragms include the order of removal on your sketch. Make a note of which side the diaphragm circular metal plate is on. Compare the parts you take off with the new ones in the kit to make sure they are the same. Put the removed parts in a separate place so you don’t mix them up with the new ones.
• Follow the same procedure with the opposite side of the carburetor using a sketch to make sure everything is in the right order. I have noticed that the carburetor manufacturer usually locates screws, tabs, bosses, etc. to allow the parts to only go back together in the correct orientation, but don’t count on it when in doubt..
• Remove the needle and spring lever. Do it slowly and carefully so that the spring doesn’t fly away. Check the needle point for damage and wipe it clean. You may want to pressure test the carburetor after assembly.
• Remove any other internal plates and parts.
• I find the most difficult part of the rebuild is the little mesh filter screen. If you feel it is too difficult to install a new one don’t mess with it or remove carefully with a dental pick.
• On the Bing carburetor, I could not remove the brass jet. It just wouldn’t turn. I left it alone.
• With all of the parts removed I check the carb body for any gasket remnants stuck to the metal. I remove them with a dental pick and one of my sharp screw drivers. I also clean off the removed plates. Keep the dental pick out of any of the orifices !!
• I now flush all of the orifices and openings in the carb body with the spray cleaner. Make sure there is nothing left in the carburetor body to fly away before you start blasting it with cleaner and compressed air. If you left the screen in, be careful in that area when you use the compressed air. After flushing I use my compressor blow gun to blow out all of the orifices and opening. I then place the carburetor in a container of clear paint thinner, swirl it around and then blow it out again.
• Clean the rest of the parts in the same manner.
• Begin your assembly process. If you removed the screen filter and it is still in good shape and clean you may want to reuse it. If so carefully place it back into the opening with a clean tweezers or screwdriver or both. If you plan to use the new screen, this is how I did it. There probably is a better way. I have a set of Harbor Freight punches of varying diameters. I picked one that is smaller than the screen detent opening. I placed the screen on the opening carefully centering it. I then centered the punch on the screen and pressed it into place. I then used a smaller punch to make sure it was thoroughly seated.
• I then put back the float needle assembly. This is very tricky because of the danger of losing the spring.
• The rest of the assembly is the reverse of the disassembly with the aid of your sketches. Clean hands, clean bench and general cleanliness are of utmost importance. I use a clean piece of newspaper on my workbench.
• The last step is putting the H and L needles and springs back in. I put a slight touch of light oil on each needle thread. I am not sure everyone agrees with this. Set up each needle with the number of turns you previously recorded.
• If you have the equipment, you may want to pressure test the carburetor. (needle and seat). Most people roll the dice on this one.
• Put the carburetor back onto the saw and you are good to go. Make sure the area around the saw is clean before you put the carburetor back on.
• I usually clean off as much dirt and grime from the outside of the carburetor especially around the springs before I take it apart. I block both the inlet and the outlet with small pieces of crumpled paper towel and spray it with carburetor cleaner using the red plastic spray tube. I then blow it clean with compressed air.
• Make sure you have a selection of small screwdrivers in good shape. Since there are still a lot of slotted screws used, make sure your slotted screwdrivers have shape edges and fill the slot of the screws. File or grind if necessary making sure the screwdrivers are clean when you are done. If you ever see a watch maker he has a large set of small screwdrivers with a stone to keep them dressed.
• I have a magnetic tray to hold the small metal parts and screws. I use a section of the tray for each section of the carburetor I take apart.
• Start with the H and L adjustment screws. Turn them in until they gently bottom out. Count the number of half turns and mark it down. This makes it easier to start the saw when the carburetor is put back on. Bag and tag each screw with its spring. On some carbs both H and L are identical. I am not sure it matters if you mix them up. But to be on the save side, I put them back the way they came out.
• There is no reason to mess with the Large Stop screw. Just clean around the spring thoroughly with your carb spray.
• Remove the pump cover. Make a sketch of the cover orientation. As you remove the gaskets and diaphragms include the order of removal on your sketch. Make a note of which side the diaphragm circular metal plate is on. Compare the parts you take off with the new ones in the kit to make sure they are the same. Put the removed parts in a separate place so you don’t mix them up with the new ones.
• Follow the same procedure with the opposite side of the carburetor using a sketch to make sure everything is in the right order. I have noticed that the carburetor manufacturer usually locates screws, tabs, bosses, etc. to allow the parts to only go back together in the correct orientation, but don’t count on it when in doubt..
• Remove the needle and spring lever. Do it slowly and carefully so that the spring doesn’t fly away. Check the needle point for damage and wipe it clean. You may want to pressure test the carburetor after assembly.
• Remove any other internal plates and parts.
• I find the most difficult part of the rebuild is the little mesh filter screen. If you feel it is too difficult to install a new one don’t mess with it or remove carefully with a dental pick.
• On the Bing carburetor, I could not remove the brass jet. It just wouldn’t turn. I left it alone.
• With all of the parts removed I check the carb body for any gasket remnants stuck to the metal. I remove them with a dental pick and one of my sharp screw drivers. I also clean off the removed plates. Keep the dental pick out of any of the orifices !!
• I now flush all of the orifices and openings in the carb body with the spray cleaner. Make sure there is nothing left in the carburetor body to fly away before you start blasting it with cleaner and compressed air. If you left the screen in, be careful in that area when you use the compressed air. After flushing I use my compressor blow gun to blow out all of the orifices and opening. I then place the carburetor in a container of clear paint thinner, swirl it around and then blow it out again.
• Clean the rest of the parts in the same manner.
• Begin your assembly process. If you removed the screen filter and it is still in good shape and clean you may want to reuse it. If so carefully place it back into the opening with a clean tweezers or screwdriver or both. If you plan to use the new screen, this is how I did it. There probably is a better way. I have a set of Harbor Freight punches of varying diameters. I picked one that is smaller than the screen detent opening. I placed the screen on the opening carefully centering it. I then centered the punch on the screen and pressed it into place. I then used a smaller punch to make sure it was thoroughly seated.
• I then put back the float needle assembly. This is very tricky because of the danger of losing the spring.
• The rest of the assembly is the reverse of the disassembly with the aid of your sketches. Clean hands, clean bench and general cleanliness are of utmost importance. I use a clean piece of newspaper on my workbench.
• The last step is putting the H and L needles and springs back in. I put a slight touch of light oil on each needle thread. I am not sure everyone agrees with this. Set up each needle with the number of turns you previously recorded.
• If you have the equipment, you may want to pressure test the carburetor. (needle and seat). Most people roll the dice on this one.
• Put the carburetor back onto the saw and you are good to go. Make sure the area around the saw is clean before you put the carburetor back on.
