Trimmer: Starts But Immediately Dies

If the carb’s settings are misadjusted, they will need to be reset to keep the engine running after it starts. Locate the carburetor underneath the air filter. Remove the covers to gain access to the carburetor. Remove the air cleaner housing and filter, and look for any obstructions in the way that could block air flow, starving the engine of oxygen. First check the operation of the choke. The choke should be closed for start up and 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 a choke problem. Next, locate the adjustment screws. To adjust the carburetor, start with both screws backed out 2 turns from the closed position. One should be idle mix and the other should be high speed. Start the engine and let it warm up for 5 minutes. 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. Hold the throttle wide open, slowly turning in the high speed until it starts to smooth out and rev high, then back this out until it starts to run rough or slows down. Turn it back in to midway between 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 more fuel when under a load, and keep your 2-cycle motor from running too lean. Put a load on it and tweak the settings a bit at a time. Make sure the oil/fuel mixture is at the proper ratio. Most will start and run with both screws open 2 turns initially. Don’t close the high speed off any more than necessary no matter how well it runs. Some carburetors are fixed, meaning they have no adjustments. Take this opportunity to clean out the carburetor with carburetor cleaner as well. They can become gummed up easily in 2-stroke engines.

You will find the air filter on top of the carb. It cleans the air flowing into the engine, and prevents small particles from entering the engine, damaging internal parts. Over time, the air filter will need to be replaced as it becomes clogged with small particles, starving the engine of air. This may lead to a starts-but-immediately-dies situation, but replacing this part should be done often anyway, as it is regular maintenance and eliminates the air filter as the future cause of this problem. Locate the air filter cover on top of the carburetor and remove it. It may be attached by screws or just a tab. Once off, remove the filter, replace it, and reassemble.

The fuel filter keeps contaminants from entering the fuel delivery system, causing problems with the fuel flow. If the fuel filter becomes heavily clogged, it will restrict the flow of fuel to the engine. Remove the gas cap, insert a small hook into the tank and pull the filter out. Inspect the filter for contaminants and blockages. If you notice any, replace the filter. Gently twist and pull the line off the filter, then install the new filter and put it back in the tank.

The gasket below the carburetor stops excess air from entering, causing the engine to run lean. To check this, start by removing the air filter and loosening the carburetor bolts. Disconnect the fuel line and remove the linkages, depending on your clearance, to remove the gasket. Check the condition of the gasket; look for tears or any indications of leaks. Clean off both mounting surfaces. The gasket will need to be replaced at this time regardless of condition, as they can only be used once. Re-install the carburetor, hook up the linkages you removed, and reconnect the fuel line. Re-install the air filter housing and air filter.

The primer bulb primes the carburetor with fuel for easier cold start ups. Usually two pushes is all it takes. If there is a crack in the primer bulb, it can draw air into the fuel, causing an improper air/fuel ratio. If the primer bulb is leaking, it can also disrupt the flow of fuel to the engine. A visual inspection of leaking gas is a good indicator as well as hearing air rush in when pushing on the bulb. To replace the bulb, simply pull it off with a pair of pliers. Next, insert a small pick back into where the bulb came off, grab the clip and pull out. Clean out the housing. Put the new clip on the primer bulb with tabs facing out. Then use a socket that fits over the primer bulb and push into the housing, giving it a gentle tap with a rubber mallet. Make sure the metal clip is as far as it can go without damaging the primer bulb. This could vary on different models, but all are similar.

If you undo the gas cap and hear air entering in, you have a vacuum inside the tank, which can cause the engine to start then die right away. See the section on “Fuel Vent” for directions on fixing this issue.

This part allows air into the fuel tank as the fuel level drops during use, if blocked, it will cause a vacuum and stop the flow of fuel. The fuel vent is located just off the 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 clamp holding it onto the lines. The best way to check it is with a vacuum tester. You can also remove the gas cap, if you hear air rushing in then you have a vacuum inside the tank. Remove and replace the vacuum vent.

A carburetor kit has everything you need to rebuild your carburetor and restore it to new condition. The carburetor kit won’t directly cause your trimmer to start and die, but it’s a solution to a failing carburetor, and that’s why we have included it on this page. Fuel that sits for a long period of time, especially mixed with oil, has the tendency to gum up the inside of a carburetor, causing fuel delivery problems. It is a good idea to take photos as you dismantle in order to make it easier for reassembly. Before beginning this repair, take photos of your carburetor for easier reassembly. Remove the air filter housing and air filter, then remove the bolts holding down the carburetor and gasket. Next, gently remove the fuel lines by twisting them and pulling, then remove the carburetor linkage. Remove the carburetor itself. Next, remove the screws on the bottom of the carburetor and pull the bottom off. Remove the gasket, diaphragm, primer bulb, and cover. On the bottom of the carburetor, notice how the lever, spring, and hinge pin fit together inside the carburetor. Remove the screw and pull these parts out of the carburetor. Clean the carburetor with carburetor cleaner making sure to get inside all the ports. Use a soft bristle brush if needed. If there is corrosion on the inside you must install a new carburetor. Install the needle and lever on the bottom of the carburetor and reinstall the screw to secure them in place. Reinstall all parts in the correct order, referring to your photos. Install the top cover and primer bulb. Reinstall the carburetor back onto the engine with a new gasket underneath. For advice on adjusting the carburetor for peak performance, see our section on this subject under the “Carburetor” header elsewhere on this page.

Fuel lines deliver the fuel from the tank to the carburetor to be mixed with the air. If the fuel line is partially blocked, it will not allow enough fuel to flow through to the carburetor. Twist and pull the fuel line off the carburetor to check the flow. If it is just dripping or no fuel is there, chase the line up till you find the blockage and replace it.