flyingtim01
ArboristSite Member
Someone on here can probably provide you with an IPL (an exploded parts list) for the 621, but changing fuel lines is pretty straight forward and cheap insurance on a 30 year old saw. First drain all the fuel from the tank, and check it for loose debris and/orvarnish. If present, clean it thoroughly using one of the many methods described. Once clean, remove the air filter and top cover (detach your coil wire and kill switch wire) and you will see the carburetor. Remove the choke rod from the carburetor (attached with a cotter pin) as well as the fuel line and you will then be able to remove the carburetor. The carburetor is attached with two bolts at the front of the carb. Remove those and remove the carburetor and air filter mount. Be careful pulling the carb away from the plastic intake manifold. A very important gasket should be there, and you'd do well not to damage it. Now you can see the fuel pump, a white plastic square held on to the body of the saw with four screws. Coming from the pump you'll see one tank vent line that terminates in the area above the clutch, as well as the shorter fuel line that connects to the inlet on the carburetor. Remove the shorter line from the pump body, you'll be replacing it. Now remove the 4 screws from the fuel pump body, and very carefully pry up at the base of the pump. Be careful not to tear the gasket. Once you get the pump up, take a close look at the gasket and make sure its not torn or cracked, if it is, you should probably replace that too. Now you'll be able to see the fuel supply line hanging from the bottom of the pump into the tank, with the fuel filter attached to the end of it. You should be able to pull the whole assembly up and out of the hole in the case. Remove the fuel filter and set it aside so you can reuse it, unless its visibly plugged with any of that old paint/epoxy in the tank, in which case you can probably clean it with some fresh fuel mix and blowing it out with compressed air. Remove the old fuel supply line from the pump and replace it with a length of new fuel line. Check to make sure that you have the right length...if its too short, when you tip the saw over the fuel will slosh away from the filter and the saw will starve for fuel. The filter needs to be able to 'swing' inside the tank so that it is always sitting in fuel no matter which way the saw is tipped/turned. Attach the fuel filter to the end of the new line, and re-seat the fuel pump and gasket on the saw body. You can check to make sure your line is long enough by removing the fuel cap and checking to make sure that at the very least, the bottom of the fuel filter is touching the bottom of the fuel tank. If so, tighten (but don't overtighten...its just plastic!) all 4 fuel pump bolts. Now replace the short fuel line that connects the pump to the carburetor. That should do it for the fuel lines. But while you've got it apart...
Check your intake gasket, this may also be your problem. Almost all intake gaskets that come with the carb kits for these carburetors are incorrect, and I'd be willing to bet that the first shop you brought it to didn't reuse the original gasket and used a new one. This saw relies on an impulse line...the action of the piston moving down in the bore creates a vacuum or impulse, and that impulse needs to be transmitted into the carburetor and fuel system in order for fuel to be sucked into the carburetor. If that system isn't sealed correctly, vacuum will be lost and fuel delivery won't operate correctly. The original carb gasket accomplishes this (it is sort of oval shaped and is a thin paper) however the newer gaskets do not (its a more triangular design and is thicker.) If there is a newer style gasket on there, it won't correctly seal the impulse passage and your saw won't run right, and may not start at all. You'll need to track down an OE style gasket, or just make one. I can scan an old gasket and email it to you, and you can then transfer that to a thick paper, like a grocery bag, and cut it out. However, if the original gasket it there and is not damaged, reuse it. Bolt your carburetor and air filter mount back up, reconnect your fuel line and choke rod. Reconnect your kill switch and coil wires, and bolt your top cover and air filter back on. Fill the tank with fresh fuel mix. Before attempting to start, check your carb adjustments. I used to work in a carburetor shop, and it was almost comical to see how some 'trained mechanics' tuned a carb. On the recoil side of the saw, you'll see a hole in the case with an L and an H cast into it, as well as corresponding mixture screws. Take a small screwdriver and slowly and gently turn both screws in until they are seated lightly. Don't crank them in hard or you will damage the needle or seat, or both, and you'll wreck your new carburetor. Once lightly seated, turn each screw out one full turn. That will be suitable to get your saw to run, and once it starts and warms up, you can further tune the Low speed and High speed settings.
Hope this helps, and if all else fails, send it to CT and I'll get it going for you!
Check your intake gasket, this may also be your problem. Almost all intake gaskets that come with the carb kits for these carburetors are incorrect, and I'd be willing to bet that the first shop you brought it to didn't reuse the original gasket and used a new one. This saw relies on an impulse line...the action of the piston moving down in the bore creates a vacuum or impulse, and that impulse needs to be transmitted into the carburetor and fuel system in order for fuel to be sucked into the carburetor. If that system isn't sealed correctly, vacuum will be lost and fuel delivery won't operate correctly. The original carb gasket accomplishes this (it is sort of oval shaped and is a thin paper) however the newer gaskets do not (its a more triangular design and is thicker.) If there is a newer style gasket on there, it won't correctly seal the impulse passage and your saw won't run right, and may not start at all. You'll need to track down an OE style gasket, or just make one. I can scan an old gasket and email it to you, and you can then transfer that to a thick paper, like a grocery bag, and cut it out. However, if the original gasket it there and is not damaged, reuse it. Bolt your carburetor and air filter mount back up, reconnect your fuel line and choke rod. Reconnect your kill switch and coil wires, and bolt your top cover and air filter back on. Fill the tank with fresh fuel mix. Before attempting to start, check your carb adjustments. I used to work in a carburetor shop, and it was almost comical to see how some 'trained mechanics' tuned a carb. On the recoil side of the saw, you'll see a hole in the case with an L and an H cast into it, as well as corresponding mixture screws. Take a small screwdriver and slowly and gently turn both screws in until they are seated lightly. Don't crank them in hard or you will damage the needle or seat, or both, and you'll wreck your new carburetor. Once lightly seated, turn each screw out one full turn. That will be suitable to get your saw to run, and once it starts and warms up, you can further tune the Low speed and High speed settings.
Hope this helps, and if all else fails, send it to CT and I'll get it going for you!
