Concrete Saw: Engine Lacks Power
If your concrete saw has an engine that lacks power, it could be due to a problem with one of the following parts: the air filter, piston ring, gasket, muffler, carburetor, armature, field, or spark plug. Use our helpful guide to determine which part you'll need to replace to have your engine back up and running. Please keep in mind that this is a general guide. For more detailed instructions on your specific model, please refer to your owner's manual.
Armatures
The armature is the rotating part of an electric motor that consists of wires wound around two or more poles of an iron core. Located on its shaft, the armature has a commutator where the carbon brushes ride on to transmit electricity. The commutator acts as a switch for the electromagnet, constantly flipping the flow of electrons at the exact moment which causes the armature to rotate.
If the armature has become damaged from overheating due to dust build up, it could cause a lack of power as a part of the armature may not be functioning.
To access the armature, begin by removing the end cap for the motor and take out the carbon brushes with a screwdriver then set aside. Take off the cover to access the motor by removing the screws and separating the covers (this will vary as all makes and models differ slightly, but will...
If the armature has become damaged from overheating due to dust build up, it could cause a lack of power as a part of the armature may not be functioning.
To access the armature, begin by removing the end cap for the motor and take out the carbon brushes with a screwdriver then set aside. Take off the cover to access the motor by removing the screws and separating the covers (this will vary as all makes and models differ slightly, but will...
The armature is the rotating part of an electric motor that consists of wires wound around two or more poles of an iron core. Located on its shaft, the armature has a commutator where the carbon brushes ride on to transmit electricity. The commutator acts as a switch for the electromagnet, constantly flipping the flow of electrons at the exact moment which causes the armature to rotate.
If the armature has become damaged from overheating due to dust build up, it could cause a lack of power as a part of the armature may not be functioning.
To access the armature, begin by removing the end cap for the motor and take out the carbon brushes with a screwdriver then set aside. Take off the cover to access the motor by removing the screws and separating the covers (this will vary as all makes and models differ slightly, but will be similar). Once you have reached the armature, pull it out.
To check for a bad armature, you can perform the 180-degree test. To do so, with the armature removed from the unit, stand it up on a bench. With an ohmmeter, attach the two ends to both sides of the commutator to measure the resistance of the windings. The reading number is not important as you move it around the commutator; you are looking for a consistence in reading, indicating all windings are good. If it varies, radically reading a zero or open circuit, then the armature is no good.
Another test is attaching the ohmmeter on each bar, adjacent to each other on the commutator, looking for a constant reading. If the ohm reads zero or open circuit, then that indicates a bad armature.
The last test is a bar to ground test which is done by placing on lead of the ohmmeter to the tip of the armature’s shaft and the other end of the ohmmeter to the commutator. If the armature is bad, install a new one. Once replaced, put the covers and brushes back on – be careful not to over-tighten the brushes as they are fragile. Finally, reinstall the end cap of the motor.
If the armature has become damaged from overheating due to dust build up, it could cause a lack of power as a part of the armature may not be functioning.
To access the armature, begin by removing the end cap for the motor and take out the carbon brushes with a screwdriver then set aside. Take off the cover to access the motor by removing the screws and separating the covers (this will vary as all makes and models differ slightly, but will be similar). Once you have reached the armature, pull it out.
To check for a bad armature, you can perform the 180-degree test. To do so, with the armature removed from the unit, stand it up on a bench. With an ohmmeter, attach the two ends to both sides of the commutator to measure the resistance of the windings. The reading number is not important as you move it around the commutator; you are looking for a consistence in reading, indicating all windings are good. If it varies, radically reading a zero or open circuit, then the armature is no good.
Another test is attaching the ohmmeter on each bar, adjacent to each other on the commutator, looking for a constant reading. If the ohm reads zero or open circuit, then that indicates a bad armature.
The last test is a bar to ground test which is done by placing on lead of the ohmmeter to the tip of the armature’s shaft and the other end of the ohmmeter to the commutator. If the armature is bad, install a new one. Once replaced, put the covers and brushes back on – be careful not to over-tighten the brushes as they are fragile. Finally, reinstall the end cap of the motor.
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Carburetors
The carburetor is designed to mix fuel and air together, providing a proper ratio for a clean and powerful combustion. If the carburetor becomes gummed up it, or out of adjustment, it can cause a lack of power.
Begin by removing the air cleaner cap, the pre-filter and air filter. Use carburetor cleaner and spray liberally around the outside, cleaning away the dirt. Open up the butterfly valve and clean out the inside, using a soft-bristle brush to clean away heavy build up. Clean thoroughly.
Next, locate the adjustment screws on the carburetor. To adjust the carburetor, start with both screws backed out two turns from the closed position. You can do this by turning both screws all of the way in, then backing off. The engine should run at these settings, but may run rough. One screw should be idle mix and the other should be high speed. Start...
Begin by removing the air cleaner cap, the pre-filter and air filter. Use carburetor cleaner and spray liberally around the outside, cleaning away the dirt. Open up the butterfly valve and clean out the inside, using a soft-bristle brush to clean away heavy build up. Clean thoroughly.
Next, locate the adjustment screws on the carburetor. To adjust the carburetor, start with both screws backed out two turns from the closed position. You can do this by turning both screws all of the way in, then backing off. The engine should run at these settings, but may run rough. One screw should be idle mix and the other should be high speed. Start...
The carburetor is designed to mix fuel and air together, providing a proper ratio for a clean and powerful combustion. If the carburetor becomes gummed up it, or out of adjustment, it can cause a lack of power.
Begin by removing the air cleaner cap, the pre-filter and air filter. Use carburetor cleaner and spray liberally around the outside, cleaning away the dirt. Open up the butterfly valve and clean out the inside, using a soft-bristle brush to clean away heavy build up. Clean thoroughly.
Next, locate the adjustment screws on the carburetor. To adjust the carburetor, start with both screws backed out two turns from the closed position. You can do this by turning both screws all of the way in, then backing off. The engine should run at these settings, but may run rough. One screw should be idle mix and the other should be high speed. Start the engine and let it warm up for five minutes, bringing the engine up to operating temperature. You may have to keep the throttle open a bit. Slowly turn in the low speed jet, until it starts to die, then back it out another 1/4 to 1/2 turn.
Next, hold the throttle wide open and slowly turn in the high speed screw. Do this until it really starts to smooth out, revs high and starts screaming. Back this out until it starts to run rough or slows down, then turn it back in, midway these two positions. Keep playing with the low speed needle until you get rapid immediate response from the throttle, and good idle with the idle adjustment.
Next, play with the high speed needle – but always back it out from the setting about 1/4 turn or so, from where it runs the smoothest. Backing it out will allow for more fuel when under a load and keep your two-cycle motor from running too lean. Put a load on it and adjust the settings a hair at a time. Also, ensure sure your oil/gas is mixed at the proper ratio. Most will start and run with both screws open two turns. Do not close the high speed off any more than necessary, no matter how well it runs. Some carburetors are fixed, meaning they have no adjustments. Reinstall the air cleaner and cover.
Begin by removing the air cleaner cap, the pre-filter and air filter. Use carburetor cleaner and spray liberally around the outside, cleaning away the dirt. Open up the butterfly valve and clean out the inside, using a soft-bristle brush to clean away heavy build up. Clean thoroughly.
Next, locate the adjustment screws on the carburetor. To adjust the carburetor, start with both screws backed out two turns from the closed position. You can do this by turning both screws all of the way in, then backing off. The engine should run at these settings, but may run rough. One screw should be idle mix and the other should be high speed. Start the engine and let it warm up for five minutes, bringing the engine up to operating temperature. You may have to keep the throttle open a bit. Slowly turn in the low speed jet, until it starts to die, then back it out another 1/4 to 1/2 turn.
Next, hold the throttle wide open and slowly turn in the high speed screw. Do this until it really starts to smooth out, revs high and starts screaming. Back this out until it starts to run rough or slows down, then turn it back in, midway these two positions. Keep playing with the low speed needle until you get rapid immediate response from the throttle, and good idle with the idle adjustment.
Next, play with the high speed needle – but always back it out from the setting about 1/4 turn or so, from where it runs the smoothest. Backing it out will allow for more fuel when under a load and keep your two-cycle motor from running too lean. Put a load on it and adjust the settings a hair at a time. Also, ensure sure your oil/gas is mixed at the proper ratio. Most will start and run with both screws open two turns. Do not close the high speed off any more than necessary, no matter how well it runs. Some carburetors are fixed, meaning they have no adjustments. Reinstall the air cleaner and cover.
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Air Filters
The air filter provides clean air for the engine by filtering out dirt and debris, preventing it from entering the engine, causing internal damage. As the air filter becomes clogged over time, it will slowly choke off needed air that is required by the engine to operate. This will cause the engine to lack power. To replace the air filter, begin by removing the cap. You may have to unscrew or unclip it to do so. There will be a foam pre-filter and a paper filter. You can wash the foam pre-filter and replace the air filter and reinstall the cover for the filter. With the amount of dust a concrete saw can produce, air filters should be checked often.
The air filter provides clean air for the engine by filtering out dirt and debris, preventing it from entering the engine, causing internal damage. As the air filter becomes clogged over time, it will slowly choke off needed air that is required by the engine to operate. This will cause the engine to lack power. To replace the air filter, begin by removing the cap. You may have to unscrew or unclip it to do so. There will be a foam pre-filter and a paper filter. You can wash the foam pre-filter and replace the air filter and reinstall the cover for the filter. With the amount of dust a concrete saw can produce, air filters should be checked often.
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Gaskets
The gasket between the carburetor and intake manifold prevents excess air from entering the engine, causing a lean fuel mixture. If this gasket is in poor shape, it can cause the engine to lack power. The vacuum created by the engine will pull excess air into the engine when trying to start, causing the air fuel mixture to be too lean.
To start, take off the top cover of the saw and disconnect the linkage for the butterfly valve. Remove the air filter cover, pre-filter and filter. Take off the mounting plate for the air filter housing and remove any carburetor linkages. This will vary on models, but is similar to other carburetor linkage. Disconnect the fuel lines, if you have to, and take out the carburetor. Check and replace the gasket or seal in between the carburetor and intake. Before installing a new gasket, or seal, clean the area...
To start, take off the top cover of the saw and disconnect the linkage for the butterfly valve. Remove the air filter cover, pre-filter and filter. Take off the mounting plate for the air filter housing and remove any carburetor linkages. This will vary on models, but is similar to other carburetor linkage. Disconnect the fuel lines, if you have to, and take out the carburetor. Check and replace the gasket or seal in between the carburetor and intake. Before installing a new gasket, or seal, clean the area...
The gasket between the carburetor and intake manifold prevents excess air from entering the engine, causing a lean fuel mixture. If this gasket is in poor shape, it can cause the engine to lack power. The vacuum created by the engine will pull excess air into the engine when trying to start, causing the air fuel mixture to be too lean.
To start, take off the top cover of the saw and disconnect the linkage for the butterfly valve. Remove the air filter cover, pre-filter and filter. Take off the mounting plate for the air filter housing and remove any carburetor linkages. This will vary on models, but is similar to other carburetor linkage. Disconnect the fuel lines, if you have to, and take out the carburetor. Check and replace the gasket or seal in between the carburetor and intake. Before installing a new gasket, or seal, clean the area with the carburetor cleaner.
Now, reinstall the carburetor by hooking the fuel line back up, linkages and replace the top gasket between the carburetor and mounting plate for the air cleaner assembly. Reconnect the mounting plate for the air filter. At this time, change the air filter, if it is dirty, and wash out the pre-filter. Put the top cover back on and reconnect the linkage to the butterfly valve. Finally, secure the top cover back down.
To start, take off the top cover of the saw and disconnect the linkage for the butterfly valve. Remove the air filter cover, pre-filter and filter. Take off the mounting plate for the air filter housing and remove any carburetor linkages. This will vary on models, but is similar to other carburetor linkage. Disconnect the fuel lines, if you have to, and take out the carburetor. Check and replace the gasket or seal in between the carburetor and intake. Before installing a new gasket, or seal, clean the area with the carburetor cleaner.
Now, reinstall the carburetor by hooking the fuel line back up, linkages and replace the top gasket between the carburetor and mounting plate for the air cleaner assembly. Reconnect the mounting plate for the air filter. At this time, change the air filter, if it is dirty, and wash out the pre-filter. Put the top cover back on and reconnect the linkage to the butterfly valve. Finally, secure the top cover back down.
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Mufflers
If a muffler becomes plugged, it will restrict the flow of air and cause low power. Signs of a muffler becoming clogged includes black smoke, a different sound from the muffler and, of course, lack of power.
To remove and clean out the muffler, or to replace it entirely, start by removing the recoil and then take off the belt cover on the blade side. Release the tension on the belt by turning the adjusting bolt counter clockwise until it stops. Take out the water line and then remove the belt by walking it off the saw blade pulley.
Now, you can remove the blade assembly. Locate the muffler and take it out. Start the engine – if it runs better without the muffler on it, and you have the symptoms previously mentioned, then the muffler is clogged. Mufflers become clogged by running rich and producing a lot of black...
To remove and clean out the muffler, or to replace it entirely, start by removing the recoil and then take off the belt cover on the blade side. Release the tension on the belt by turning the adjusting bolt counter clockwise until it stops. Take out the water line and then remove the belt by walking it off the saw blade pulley.
Now, you can remove the blade assembly. Locate the muffler and take it out. Start the engine – if it runs better without the muffler on it, and you have the symptoms previously mentioned, then the muffler is clogged. Mufflers become clogged by running rich and producing a lot of black...
If a muffler becomes plugged, it will restrict the flow of air and cause low power. Signs of a muffler becoming clogged includes black smoke, a different sound from the muffler and, of course, lack of power.
To remove and clean out the muffler, or to replace it entirely, start by removing the recoil and then take off the belt cover on the blade side. Release the tension on the belt by turning the adjusting bolt counter clockwise until it stops. Take out the water line and then remove the belt by walking it off the saw blade pulley.
Now, you can remove the blade assembly. Locate the muffler and take it out. Start the engine – if it runs better without the muffler on it, and you have the symptoms previously mentioned, then the muffler is clogged. Mufflers become clogged by running rich and producing a lot of black smoke and soot. Over time, this soot builds up in the muffler and slowly clogs it. Spray carburetor cleaner inside of it and shake it to dry. If rusty particles appear, or you notice any cracks, your muffler needs to be replaced. Use compressed air to blow it dry, including the inside, and reinstall (or install a new one if required). Put the water line back in the saw, followed by the blade assembly. Reattach the belt around the blade pulley by walking it back on the pulley. Reapply the tension by turning the adjusting bolt clockwise until it stops.
Next, reinstall the belt cover and then the recoil. Readjust your carburetor settings to prevent the engine from running rich, avoiding the same problem from occurring. See “carburetor” on how to adjust these settings.
To remove and clean out the muffler, or to replace it entirely, start by removing the recoil and then take off the belt cover on the blade side. Release the tension on the belt by turning the adjusting bolt counter clockwise until it stops. Take out the water line and then remove the belt by walking it off the saw blade pulley.
Now, you can remove the blade assembly. Locate the muffler and take it out. Start the engine – if it runs better without the muffler on it, and you have the symptoms previously mentioned, then the muffler is clogged. Mufflers become clogged by running rich and producing a lot of black smoke and soot. Over time, this soot builds up in the muffler and slowly clogs it. Spray carburetor cleaner inside of it and shake it to dry. If rusty particles appear, or you notice any cracks, your muffler needs to be replaced. Use compressed air to blow it dry, including the inside, and reinstall (or install a new one if required). Put the water line back in the saw, followed by the blade assembly. Reattach the belt around the blade pulley by walking it back on the pulley. Reapply the tension by turning the adjusting bolt clockwise until it stops.
Next, reinstall the belt cover and then the recoil. Readjust your carburetor settings to prevent the engine from running rich, avoiding the same problem from occurring. See “carburetor” on how to adjust these settings.
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Spark Plugs
The spark plug produces the spark to ignite the air/fuel mixture inside the combustion chamber. Badly worn, damaged or broken spark plugs will cause the engine to lack power. To check the condition of the spark plug, carefully remove the spark plug boot by twisting and pulling until it releases. Inspect the spark plug – it should be light grey or brown for normal conditions. You can clean and re-gap this plug to use it again but it is always best to replace them as they are inexpensive and should be changed regularly. If the plug has deposits, corrosion, melting, eroding or wet fouling, the plug must be replaced. Once replaced, the engine should be fixed of the issue causing the plug to malfunction.
The spark plug produces the spark to ignite the air/fuel mixture inside the combustion chamber. Badly worn, damaged or broken spark plugs will cause the engine to lack power. To check the condition of the spark plug, carefully remove the spark plug boot by twisting and pulling until it releases. Inspect the spark plug – it should be light grey or brown for normal conditions. You can clean and re-gap this plug to use it again but it is always best to replace them as they are inexpensive and should be changed regularly. If the plug has deposits, corrosion, melting, eroding or wet fouling, the plug must be replaced. Once replaced, the engine should be fixed of the issue causing the plug to malfunction.
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Brushes
Brushes provide the electrical current to the armature by riding on the commutator. If these brushes are damaged, or worn down and wear out, it can impact their ability to provide the electrical current to the commutator and cause the motor to lack power. To solve this issue, start by taking off the motor end cap and locate the brush caps. Detach the brush caps with a screwdriver and remove the brush from the motor. If the brush is damaged from overheating, you may need to use a small screwdriver and pliers to pull out and break what is left of the carbon brush. Clean out the inside and insert the new brush by aligning the wings on the end of the brush with the holder. Hold the brush in place and reinstall the cap. Do not over tighten the cap, as it can break easily.
Brushes provide the electrical current to the armature by riding on the commutator. If these brushes are damaged, or worn down and wear out, it can impact their ability to provide the electrical current to the commutator and cause the motor to lack power. To solve this issue, start by taking off the motor end cap and locate the brush caps. Detach the brush caps with a screwdriver and remove the brush from the motor. If the brush is damaged from overheating, you may need to use a small screwdriver and pliers to pull out and break what is left of the carbon brush. Clean out the inside and insert the new brush by aligning the wings on the end of the brush with the holder. Hold the brush in place and reinstall the cap. Do not over tighten the cap, as it can break easily.
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Rings
There are rings located around the piston, creating a seal between the piston and the cylinder. Piston rings cause a tight seal that produces compression in the combustion chamber. If they wear out, the pressure in the combustion chamber will drop and cause the engine to lose significant power as the air/fuel mixture will blow by the rings.
To check the piston rings, start with a compression test using a compression test gauge. Remove the spark plug and attach the compression gauge. Turn the engine over and check the reading on your gauge. Refer to the owner’s manual, or repair manual, for your model’s specifications. Write down the number from your test and compare that number to what the manufacturer’s specifications are. If there is a big difference that is a good indication the rings are bad. To confirm, add a little oil inside the cylinder. Oil will take up...
To check the piston rings, start with a compression test using a compression test gauge. Remove the spark plug and attach the compression gauge. Turn the engine over and check the reading on your gauge. Refer to the owner’s manual, or repair manual, for your model’s specifications. Write down the number from your test and compare that number to what the manufacturer’s specifications are. If there is a big difference that is a good indication the rings are bad. To confirm, add a little oil inside the cylinder. Oil will take up...
There are rings located around the piston, creating a seal between the piston and the cylinder. Piston rings cause a tight seal that produces compression in the combustion chamber. If they wear out, the pressure in the combustion chamber will drop and cause the engine to lose significant power as the air/fuel mixture will blow by the rings.
To check the piston rings, start with a compression test using a compression test gauge. Remove the spark plug and attach the compression gauge. Turn the engine over and check the reading on your gauge. Refer to the owner’s manual, or repair manual, for your model’s specifications. Write down the number from your test and compare that number to what the manufacturer’s specifications are. If there is a big difference that is a good indication the rings are bad. To confirm, add a little oil inside the cylinder. Oil will take up space between the rings and the wall. Turn the engine over for a second time and take a reading. If the reading goes up, your rings are bad and need to be replaced.
To replace, you will have to tear down the engine. Begin by removing the recoil. Take off the belt cover and release the tension on the belt. Turn your saw on its side and disconnect the water line. Remove the belt from the pulley and the blade. Take off the muffler and inspect the piston and rings for damage by looking through the exhaust port. Remove the top cover and disconnect the linkage for the butterfly valve on this cover.
Next, take off the handle and then the spark plug, ensuring the spark plug wires are out of the way. Take off the cover over the engine as well as the side cover. Remove the bottom crank case bolts. Take out the intake boot from the cylinder by loosening the clamp on the boot and removing it. Using a dull flat-head screwdriver, pry the boot off gently. Now, you can take off the cylinder head sleeve by twisting it back and forth, pulling upwards. You can use a small flat-blade screwdriver to remove the piston rings.
Install the new piston rings by pushing them over the piston, positioning the ring gaps 1/3 a part from each other to prevent blow by. Apply clean engine oil to the cylinder head sleeve and reinstall. These parts are small enough that you can just use your hands to push the rings together to get them in the cylinder. Once reinstalled, fasten it back down. Reinstall the boot and clamp, and then tighten the clamp down. Reinstall the bottom crank cause bolts and tighten according to the manufacturer’s specifications. Put the top and side covers back on and reattach the spark plug wires and switch wires. Reattach the handle and the outer top cover, reconnecting the linkage for the butterfly valve. Put the muffler on and install the belt around the pulley. Reinstall the blade and reapply the tension. Connect the water line and put the belt cover on. Lastly, reinstall the recoil.
To check the piston rings, start with a compression test using a compression test gauge. Remove the spark plug and attach the compression gauge. Turn the engine over and check the reading on your gauge. Refer to the owner’s manual, or repair manual, for your model’s specifications. Write down the number from your test and compare that number to what the manufacturer’s specifications are. If there is a big difference that is a good indication the rings are bad. To confirm, add a little oil inside the cylinder. Oil will take up space between the rings and the wall. Turn the engine over for a second time and take a reading. If the reading goes up, your rings are bad and need to be replaced.
To replace, you will have to tear down the engine. Begin by removing the recoil. Take off the belt cover and release the tension on the belt. Turn your saw on its side and disconnect the water line. Remove the belt from the pulley and the blade. Take off the muffler and inspect the piston and rings for damage by looking through the exhaust port. Remove the top cover and disconnect the linkage for the butterfly valve on this cover.
Next, take off the handle and then the spark plug, ensuring the spark plug wires are out of the way. Take off the cover over the engine as well as the side cover. Remove the bottom crank case bolts. Take out the intake boot from the cylinder by loosening the clamp on the boot and removing it. Using a dull flat-head screwdriver, pry the boot off gently. Now, you can take off the cylinder head sleeve by twisting it back and forth, pulling upwards. You can use a small flat-blade screwdriver to remove the piston rings.
Install the new piston rings by pushing them over the piston, positioning the ring gaps 1/3 a part from each other to prevent blow by. Apply clean engine oil to the cylinder head sleeve and reinstall. These parts are small enough that you can just use your hands to push the rings together to get them in the cylinder. Once reinstalled, fasten it back down. Reinstall the boot and clamp, and then tighten the clamp down. Reinstall the bottom crank cause bolts and tighten according to the manufacturer’s specifications. Put the top and side covers back on and reattach the spark plug wires and switch wires. Reattach the handle and the outer top cover, reconnecting the linkage for the butterfly valve. Put the muffler on and install the belt around the pulley. Reinstall the blade and reapply the tension. Connect the water line and put the belt cover on. Lastly, reinstall the recoil.
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