Concrete Saw: Starts, Runs for a While, Then Dies

The fuel vent allows air into the fuel tank as the fuel level drops during use. If blocked, it will cause a vacuum, stopping the flow of fuel. To check for a blockage, locate the fuel vent just off the fuel tank. It will be attached to a fuel line, entering the tank through a grommet with the fuel delivery and return lines. Once located, simply pull off the clamps holding it on the lines. The best way to check is with a vacuum tester. You can also remove the gas cap – if you hear air rushing in, you have a vacuum inside the tank. Remove and replace the vacuum vent. For some systems, and depending on your model, the vent is part of the cap so you can just replace the cap to solve the problem.

The carburetor is designed to mix fuel and air in the proper mixture for combustion. If the settings become unadjusted, you will need to reset them in order to keep the engine running after it starts.
Locate the carburetor underneath the air filter. Remove any covers necessary to gain access to the carburetor. Take out the air cleaner housing and filter. First, check the operation of the choke. The choke should be closed for start up and for the first few minutes, as the engine warms up. If the choke comes off too soon, it will cause the engine to die. If the cable is stretched, replace it by disconnecting it at both ends and installing a new one. This should solve the choke problem. Check that the linkage is not bent out of shape, impacting operation of the carburetor. Now, locate the adjustment screws.
To adjust the carburetor, start with both screws backed out two turns from the closed position. One should be idle mix and the other high speed. Start the engine, allowing it to warm up for five minutes. You may have to keep the throttle open a bit, allowing the engine to keep running. Slowly turn in the low speed jet, until it starts to die, then back it out another ¼ or ½ turn.
Next, hold the throttle wide open and slowly turn in the high speed, until it really starts to smooth out, rev high, and starts screaming. Then, back this out until it starts to run rough or slows down. Turn it back in midway between these two positions. Keep playing with the low speed needle until you get a rapid, immediate response from the throttle and a good idle with the idle adjustment.
Next, play with the high speed needle, but always back it out from the setting – about ¼ turn or so – from where it runs the smoothest. This setting of backing it out will allow more fuel when under a load and keep your two-cycle motor from running too lean. Next, put a load on it and tweak the settings, just a tiny bit at a time. Also, make sure the oil/fuel is mixed at the proper ratio. Most will start and run with both screws open two turns.
Do not close off the high speed any more than necessary, no matter how well it turns. Some carburetors are fixed, meaning they have no adjustments. Clean out the carburetor with carburetor cleaner as they can easily become gummed up in a two-stroke engine.

The air filter cleans the air of all contaminants from entering the engine, causing internal damage to vital engine parts. If the engine runs for a while, then dies, check your air filter. Concrete saws can give off a lot of dust, which can quickly clog the air filter if you’re not using water to keep the dust down. Remove the cleaner cap, filter and pre-filter. The pre-filter can be washed; it is foam and designed for this purpose on a machine that produces a lot of dust. Wash the pre-filter and replace the paper filter and reinstall.

The fuel filter filters out debris that may have entered the tank, preventing it from entering the carburetor and engine, causing further issues with the engine. Check the fuel filter for an obstruction by inserting a small hook in the fuel tank, pulling the fuel line up. The filter is located at the end of the line. Twist and pull gently to remove the fuel filter and install a new one. Insert the new fuel filter back in the tank and seal with the cap.

The muffler silences the noise made by the internal combustion engine. If the engine is running rich, it will create black, sooty smoke. This will build up inside the muffler and prevent it from running as it slowly chokes off the flow of exhaust, backing it up in the engine.
To remove and check the muffler, 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 by turning the saw on its side to access the bolt. Walk the belt off the saw pulley and then remove the blade assembly.
Locate the muffler and take it out. Now, start the engine. Let it run for a while and observe. If it appears to run fine without the muffler, try cleaning out the old muffler with carburetor cleaner and dry it with compressed air. Shake it – if you hear any noise or rust particles are falling out, then replace it.
Install the new, or cleaned muffler, back in the engine. Put the water line back on 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 nut clockwise until it stops. Put the belt cover and recoil back on.
Readjust your carburetor settings to prevent the engine from running rich, causing the same problem to occur. See “carburetor” on how to adjust these settings.

The spark plug ignites the air/fuel mixture in the combustion chamber. A malfunctioning plug can stop the engine from running. To check the spark plug, remove the wire from the spark plug – be careful doing this as they are fragile. Remove the spark plug and check the condition. Sometimes, on a two-stroke engine, they can get oily build up from improper oil gas mixture which can cause the spark not to jump. Clean the plug and re-gap to the manufacturer’s specifications. Be sure to check for any deposit, breakage, melted and corrosion. If you see any of these symptoms, replace the plug and gap to manufacturer’s specifications. Ensure your oil and fuel are mixed to the proper ratio, as this can impact operation of the spark plug. If your engine spends most of the time running at high RPMs, try installing a cooler-running plug for quicker heat dissipation. A hotter running-plug can cause the spark plug to fowl, after it has been running for a while. This will prevent the engine from running any further, until the engine backs down.

The fuel vent allows air into the fuel tank as the fuel level drops during use. If blocked, it will cause a vacuum, stopping the flow of fuel. To check for a blockage, locate the fuel vent just off the fuel tank. It will be attached to a fuel line, entering the tank through a grommet with the fuel delivery and return lines. Once located, simply pull off the clamps holding it on the lines. The best way to check is with a vacuum tester. You can also remove the gas cap – if you hear air rushing in, you have a vacuum inside the tank. Remove and replace the vacuum vent. For some systems, and depending on your model, the vent is part of the cap so you can just replace the cap to solve the problem.

The coil produces the current for the spark plug by using magnets on the flywheel, rotating pass the magnets on the coil. If the engine runs for a while, then dies, you may have a module that is slowly dying, or is weak. To check for this, hook up a spark plug tester to the spark plug wire that is coming off the coil. Turn over the engine and look for a spark. If there is no spark, check the connections on the module to see if they are tight. To replace the coil, unplug the wires going to it (including the spark plug wire). Remove the bolts that are securing it in place and discard the old coil. Install the new coil hand tight and insert a business card between the flywheel and the coil. Rotate the flywheel in place so that the magnets line up with the coil. Let the magnets on the flywheel pull the coil in place. Tighten the bolts, securing it in place, and remove the business card. Hook all the wires back up to the coil.

The fuel line delivers fuel from the tank to the carburetor. In most cases, a fuel line will not cause the engine to die after it has been running for a while. However, if the machine has been poorly maintained and the fuel lines have been deteriorating over time, it can contribute to the cause. Check the condition of the fuel lines – if they are badly weathered, or cracked, they need immediate attention as they can start leaking and become a fire hazard. The inside of the lines could be breaking down or clogging up the inside. Also, as it breaks down, little particle can flow into the carburetor. Check the lines for blockage by removing and looking for fuel to flow out. Check the condition of the fuel flowing to see if it is discoloured or any debris is coming out. Replace the lines.