Engine: Starts But Immediately Dies

The purpose of the carburetor is to mix air and fuel together to the proper ratio for combustion. A carburetor that has a heavy buildup of dirt can cause the engine to die immediately after start-up. Fuel that sits for a long period of time can also gum up the inside of a carburetor. To check the carburetor, remove the air cleaner assembly and filter, and inspect the inside. Open the choke and inspect it as well. Now, spray carburetor cleaner inside the carburetor, use a soft bristle brush to remove heavy build up, then re-check the engine.

The air filter is located on top of the carburetor. It cleans the air flowing into the engine and prevents small particles from causing internal damage. Over time, the air filter will need to be replaced as it becomes clogged with small particles and starves the engine of air. This is more likely to cause a no-start situation but it may cause the engine to die immediately after it starts as well. To clean and/or replace the air filter, locate the air filter cover on top of the carburetor and remove it. It may be attached by screws or just a tab. Once the cover is off, remove the filter, replace it with a new one, and re-assemble. This should be done as part of a regular maintenance schedule to prevent further problems.

The gasket below the carburetor stops excess air from entering the engine and causing it to run lean. Start by removing the air filter, and loosening the carburetor bolts. Next, disconnect the fuel line, remove any linkages, and remove the gasket. Now, you can check the condition of the gasket, looking for tears, rips, or any indications of leaks. Next, clean off both mounting surfaces. Replace the gasket, re-install the carburetor, and hook up any linkages you removed. Then, remove and reconnect the fuel line. Finally, re-install the air filter housing and air filter.

The primer bulb primes the carburetor with fuel for easier cold start-ups. If there is a crack in the primer bulb, it can draw air into the fuel causing an improper air/fuel ratio. Also, if the primer bulb is leaking, it can disrupt the flow of fuel to the engine. Noticeable leaking gas or the sound of air rushing in when the bulb is pushed are a good indicator that the bulb is cracked. To replace the bulb, simply pull it off with a pair of pliers. Next, grab a small pick and reach back into where the bulb came off, grab the clip, and pull out. Next, clean out the housing, then put the new clip on the primer bulb with the tabs facing out. Use a socket that fits over the primer bulb, push it into the housing and tap it gently with a rubber mallet. Make sure the metal clip is as far in as it can go without damaging the primer bulb.

The fuel cap keeps fuel in the tank and keeps debris out. A lot of caps have a vent on them to allow air in as the fuel goes down. If the vent is not working, it can create a vacuum inside the tank, which will stop the flow of fuel. Remove the cap, and if you hear air entering the tank, you have a vacuum inside the tank. Change the cap to complete this repair.

Some engines have a carburetor that has a diaphragm inside it, and it pumps fuel from the tank to the carburetor. Over time, fuel can cause the diaphragm to deteriorate and this will result in fuel not being delivered to the carburetor quickly enough. This can cause the engine to die immediately after it starts. To fix this issue, first remove the air filter housing assembly and set it aside. Remove the carburetor from the engine by unbolting it, and pinch off the fuel lines to prevent a fuel spill. Then, remove the fuel lines, the carburetor and then the linkage. Next, you will need to remove the gasket under the carburetor, as well as the screws on the bottom of the carburetor, to pull the bottom off. Remove the gasket and the diaphragm and install the new gasket with a new diaphragm. Reinstall the cover back onto the carburetor, hook the linkage back up to the carburetor, and re-install the carburetor onto the engine with a new gasket underneath it. Then, re-attach the fuel line back onto the carburetor, making sure to un-pinch the fuel line. Finally, re-attach the air filter housing and filter.

A carburetor kit contains everything you need to rebuild and restore your carburetor. To install a carburetor kit, first remove the air filter housing and the air filter. Remove the bolts holding down the carburetor and gasket and pinch off the fuel line to prevent a fuel spill. Next, remove the fuel lines by twisting them gently and pulling them off, then remove the carburetor and disconnect the linkage. Start your carburetor disassembly by removing the nut on the bowl, then separating the bowl from the carburetor, and removing the gasket or O-ring. Then, remove the float pin and the needle valve. Unscrew the main jet screw and dump it out with the emulsion tube. Then, remove the plastic throttle stop and the metering plug from the carburetor. Next, spray the carburetor, fuel bowl and all the small orifices with carburetor cleaner and wipe clean. If you notice any corrosion inside the carburetor or the bowl, it will need to be replaced. Now, re-install a new emulsion tube and main jet, and tighten them. Install a new metering plug, re-install the throttle stop screw and thread it until it sticks out the other side about 1/16 of an inch. Next, install the new spring on the needle valve, snap the new needle valve into the float, and re-attach the float to the carburetor by sliding the new pin in. Install the new bowl O-ring, re-install the bowl, and tighten them down. Now, re-install the carburetor with a new intake gasket, reattach the linkage and the fuel line. Remember to un-pinch the fuel line before you install it again. Now, re-attach the air filter assembly with the filter. Once you’ve completed the repair, you will need to adjust the carb. To do this, first locate both idle screws on the carburetor, one marked L (low) and one marked H (high). Turn both screws all the way in, and shut off fuel. Then reverse them two full turns. Now, start up the engine, and allow it to idle for a few minutes. Turn the L screw clockwise until the engine slows down, then turn it in the opposite direction until it slows down again. Set the screw at the approximate midpoint of these 2 spots. Using a tachometer to gauge engine speed, set the idle speed screw to bring the engine to 1750 RPM for an aluminum-cylinder engine or 1200 RPM for an engine with a cast-iron cylinder sleeve. Next, at full throttle, turn the high speed or main jet screw clockwise until the engine begins to slow. Then, turn the screw the other way until the engine slows again. Turn the screw back to the midpoint and your adjustments are complete. Once adjusted, check the engine acceleration by moving the throttle from idle to fast. The engine should accelerate smoothly.