Engine: Won't Start

Engines with an electric start will have a starter. The gear on the starter is called a pinion gear, and it meets the flywheel gear to turn the engine over and start it. If the pinion gear is damaged and can no longer spin the flywheel gear, then you should replace the gear. To do so, you may want to purchase a rebuild kit for your starter, as it contains all new parts for replacing the gear. To complete the repair, disconnect the battery, and remove the wires at the starter. Then, unbolt the starter and remove from the unit. Using pliers, remove the clip at the end of the starter shaft and remove the spring. Use a hammer and a small punch to drive the dowel out of the starter shaft. Remove all the parts and the gear, but keep them in line so you know the order they will be re-installed in, or even better, take pictures as you go. Next, insert the bottom piece and spin the new gear on with the bevels on the gear pointed upwards. Then, slide the bottom piece with the gear back onto the starter shaft. Install the top piece then hammer the dowel into position to secure it, making sure it is flush. Install the cap and spring back onto the shaft, then re-install the retaining clip back on to the shaft by gently tapping it into place. Now, re-install the starter back onto the engine, hook the wires back up, and reconnect the battery.

The springs hold the valves in your engine closed. If a spring has broken, it will not be able to close the valve tightly. This can result in a no-start situation, but if the valve has dropped into the cylinder, then the problem is a catastrophic failure. A valve falling into the cylinder will destroy the piston, the valve, the connecting rod, the cylinder head, and will badly damage the cylinder walls. When this occurs, you will require a new engine. If the spring is broken and still holding the valve, then it can be fixed. To check for a broken spring, remove the valve cover and inspect the springs. A broken spring will be noticeable. If you notice a broken spring, remove the air filter assembly, the carburetor, the muffler, and the valve cover and gasket from the engine, then remove the spark plug. Rotate the piston to top dead center, making sure the magnets on the flywheel are in line with the ignition coil. Remove the jam nuts securing the pivots and remove the rocker arm pivots and the arms themselves. Next, pull out the push rods, remove the rocker arm studs, and pull out the guide plate. Next, remove the cylinder head bolts in a diagonal pattern so you do not warp the cylinder head. Then, remove the cylinder head and place it on a bench. Use pliers to remove the valve spring retainers and the springs. On older non-OHV engines, you will have to remove the access panel on the side of the engine to expose the valves, and insert the spring compressor inside to compress the spring. Then, rotate the valve around the retainer to lift the valve and remove the broken spring. Install the spring and retainer, locking it into position on the valve. Clean off the surfaces for the new head gasket, then re-install the cylinder head onto the engine, tightening the bolts down in an alternating pattern to avoid warping the cylinder head. Reinstall the guide plate and rocker arm studs, and torque them down. Insert the push rod, slide on the rocker arms, and thread the pivots loosely. Use a feeler gauge to gap the rocker arms 3-5 thousandths of an inch from the valves. Next, thread the jam nuts, tighten them down, and re-install the spark plug. Then, install a new valve cover gasket and re-install the valve cover. Tighten the bolts in an alternating pattern, to the manufacturer’s specifications. Re-install the muffler and the carburetor with the air filter housing and filter, and the repair is complete.

The stop switch prevents the engine from starting unless you insert the key. This switch prevents the spark plug from receiving current when the key is removed. You should replace the stop switch if the engine runs when the key is removed, or the switch prevents the plug from sparking when the key is inserted. To replace the stop switch, first remove any covers to gain access to the rear of the stop switch (this will vary on every model). Next, disconnect the wires on the back, press in the tabs holding it in place, and remove it. Install the new switch by snapping it in place and hooking up the wires. Also, re-install any covers that you have removed to gain access to the stop switch.

Every engine contains at least one intake valve and one outtake valve. The intake valve is always the larger one. These valves control the flow of the air/fuel mixture entering the combustion chamber, as well as expelling the exhaust gases. A bent valve stem on a valve will prevent it from opening all the way. To check if the valves are operating correctly on a single-cylinder engine, turn the engine over and hold one hand in front of the exhaust. If you feel air coming out, then they are operating properly. If not, then 1 or more valves are closed. On multiple-cylinder engines, you will have a constant miss at all speeds. To install new valves on an OHV engine, remove the carburetor, muffler, and the valve cover from the engine, then remove the spark plug. Rotate the piston to top dead center, making sure the magnets on the flywheel are in line with the ignition coil. Next, remove the jam nuts securing the pivots, then remove the rocker arm pivots and the arms. Next, remove the push rods and the rocker arm studs, and pull out the guide plate. Now, remove the cylinder head bolts in a diagonal pattern so you do not warp the cylinder head, then place it on a bench. Use pliers to remove the valve spring retainers and springs, then remove the valve from the cylinder head. Use some fine valve lapping compound on the valve seat and cylinder head to get the new valves to seat properly. Then, insert the valves into the head and use a lapping tool to seat them by rotating the lapping tool in your hands, back and forth. Next, remove the valves and clean the lapping compound off the valve and cylinder head. Lubricate the valve stems with oil and insert them into the cylinder head. Next, install the new seal on the valve, then install the spring and retainer, and lock the retainer into position on the valve. Clean off the surfaces for the new head gasket and re-install the cylinder head by tightening the bolts down in an alternating pattern. Now, re-install the guide plate and rocker arms studs, then torque to the manufacturer’s specifications. Insert the push rod, slide on the rocker arms, and thread the pivots loosely. Use a feeler gauge to gap the rocker arms 3 to 5 thousandths of an inch. Thread the jam nuts and tighten them down, then re-install the spark plug. Install a new valve cover gasket and re-install the valve cover. Tighten bolts in an alternating pattern, then re-install the muffler and the carburetor with the air filter housing and filter.

The carburetor mixes air and fuel together in the proper mixture for combustion. If it is clogged or damaged, you will need to clean or replace it before your engine will start. To inspect or repair the carburetor, first locate the bolts securing the carburetor onto the engine and air intake and remove them. Next, carefully remove the choke lever, then remove the fuel line at the carburetor to check for fuel flow. If the fuel is flowing, pinch it off to prevent a spill and then carry on to the carburetor. If there is no fuel flowing when you remove the line, then continue to diagnose the problem through the fuel delivery system. Continuing with the carburetor, next slide the choke control plate off the carburetor and disconnect the linkage from the control plate and the carburetor. Next, disconnect the throttle rod return spring, and remove the throttle rod from the carburetor. Next, clean out the carburetor, using carburetor cleaner and a soft brush for the inside, then reinstall the carburetor. You will also need to check that the choke valve is functioning properly. It should be closed to allow the air/fuel mixture to be rich for starting. If the cable has become stretched, then replace it by locating the mounting points on each end, removing the cable from these points and replacing it with a new cable. Check that all the springs are there, and that none have broken off. Refer to a repair guide for your model for proper spring hook-up.

A heavily clogged air filter will prevent the flow of air into the engine for combustion. This can cause a no-start situation. To solve this issue, check the filter and replace as necessary. It is recommended to change your air filter annually to prevent this problem.

The fuel pump forces the fuel from the tank to the engine. Most small engine fuel pumps are vacuum-fed. To check the operation of the pump, first remove the inlet line at the pump, and check for fuel flow. If fuel is present, re-attach and remove the line at the carburetor, turn the engine over and inspect for fuel flowing out of the fuel line. If there is no fuel flowing from the line, then check the line for a clog. If there is no clog and the pump is receiving fuel, then the next step is to check your vacuum line for cracks or leaks. If the vacuum line has a leak, the pump will be inoperative, and you will need to replace the line. If the pump is still inoperative, then you will need to replace the pump. To do so, first drain the fuel from the tank. Remove the bolts securing the fuel pump and remove the fuel and vacuum lines. Finally, attach the lines to the new fuel pump, fasten the pump to the engine, and add the fuel back to the tank.

The purpose of a gasket is to create a tight seal between two joining pieces, and seal off air and fluids from entering areas where they are not supposed to be. A damaged gasket below the carburetor will pull excess air into the cylinder, causing the air/fuel mixture to be lean, and preventing the engine from starting. To replace the gasket, first remove the air filter housing and remove the bolts securing the carburetor in place. Remove any linkages and the fuel line, but remember to pinch off the fuel line ahead of time to prevent leakage. Now, check the condition of the gasket. You are looking for tears, rips, or any indications of leaks. Gaskets can only be used once, so you will have to replace it at this point, regardless of its condition. Now, clean both mating surfaces where the gasket will be positioned. Reinstall the carburetor, hooking up the linkages and the fuel line. Un-pinch the fuel line to allow the fuel to flow and re-install the air filter assembly.

The spark plug ignites the air/fuel mixture in the combustion chamber. Any build-up on a spark plug can ground it out, and prevent it from firing. Oily build-ups are very common on 2-stroke engines, and are caused by an improper mixture of oil and fuel. However, this is not a common problem on a 4-stroke engine. To check condition of the spark plug, look for deposits, corrosion, erosion, melting, or oxidization. If any of these symptoms are present, you will need to replace it, as they can impact the operation of the spark plug. If the spark plug just has an oily build up, then cleaning it off should get it working properly again.

The purpose of the starter is to turn the engine over, and allow it to run on its own. Pulling the rope engages the pawls inside the starter, which lock onto the flywheel and turn the engine over. The recoil spring then retracts the rope. Replacing the starter is the quickest and the easiest way of getting your engine to run again without repairing the pieces of the starter individually. To replace the starter, remove the bolts holding it down, then remove it. Now, install the new starter and your repair is complete.

The primer bulb pumps fuel into the carburetor to make it easier for the engine to start up when it’s cold. Pushing it twice is usually all you will need to get the engine running. If the primer bulb is cracked, leaking fuel, or you can hear air entering when it is pushed, then the primer bulb is not functioning properly and it will need to be replaced. To replace the primer bulb, start by using a small flat-head screwdriver to pry out the old primer bulb. Then, install a new primer bulb by using a larger flat-head screwdriver to carefully tuck the edges back into place in the groove. On some models, there may be a clip around the bulb that you can remove with snap-ring pliers. On other models, you may have to remove the cover that the primer bulb is housed in, to remove it from the back. You will also need to disconnect the fuel line and push the pins in with pliers to remove the unit. Once removed, pull off the old primer bulb and re-install the new bulb, then re-install it into the cover. Remember to hook the fuel line back up, then re-install the cover onto the machine.

The diaphragm regulates fuel in the mixture, and is located inside the carburetor. Over time, this diaphragm will start to deteriorate and can cause the fuel not to be delivered to the engine. This will prevent your engine from starting. To fix the diaphragm, first remove the air filter housing assembly. Remove the carburetor from the engine and pinch off the fuel lines to prevent a fuel spill. With the line pinched, you can now pull it off. Next, remove the carburetor, linkage, and the gasket under the carburetor. Remove the screws on the bottom of the carburetor and pull the bottom off. Then, remove the gasket and the diaphragm and install the new gasket with a new diaphragm. Re-install the cover back onto the carburetor, hook the linkage back up to the carburetor, then re-install the carburetor with a new gasket underneath it. Re-attach the fuel line, but remember to un-pinch the line so fuel will flow. Finally, re-attach the air filter housing and filter.

The push rod rides on the lobes of the camshaft, which is driven by the crankshaft. It transfers power from a rotary motion to a reciprocating motion. The top of the push rod pushes on the rocker arm, which then pivots, and the other end of the rocker arm pushes on the top of the valve, opening the valves. This allows the air/fuel mixture into the combustion chamber, and the exhaust to leave the combustion chamber. If a push rod becomes bent, it will impact how much these valves open. A badly bent rod can disable the engine altogether, since the valve will remain closed. To diagnose, remove the engine valve cover with the valve cover gasket. Then, remove the jam nuts and loosen the pivots. Rotate the rocker arms to the side, and pull out the push rods. A bent rod will be noticeable, and will need to be replaced with a new one. Be sure to add some engine oil to the rod before installing it. Now, rotate the rocker arms back into position, and hand-tighten the pivots. Now, set the gap with the pivots between the rocker arms and valve tip from 3- 5 thousandths of an inch, and tighten the jam nuts down. Finally, replace the valve cover gasket with a new one, and reinstall the valve cover.

The pivot arm in your engine helps to control the valves. If the arm becomes damaged or broken, it will impact its operation of controlling these valves. To check the arms, first remove the valve cover and inspect for a damaged arm. Once located, remove the hold down bolt and the jam nut. At this point, remove the old arm and replace it with a new one. Hand-tighten the pivot, then use a feeler gauge and set the gap from 3 to 5 thousandths of an inch. Now, re-install the jam nut and hold the pivot in place with a wrench as you tighten the jam nut up against it. Re-install the valve cover with a new valve cover gasket. You will need to do so in an alternating pattern, and to the manufacturer’s specifications to prevent warping.

Carburetor kits are made up of the parts you need to rebuild your carburetor and restore it to working condition. To access the carburetor, start by removing the air filter housing unit. Pinch off the fuel line to prevent fuel from flowing, then remove the fuel line. Locate the bolts securing the carburetor to the engine and air intake, remove them, then disconnect the linkages from the carburetor. The carburetor should now slide right off. Lie the carburetor on a bench and start disassembly by removing the nut on the bowl, then removing the bowl and gasket. Next, 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. Spray the carburetor, fuel bowl and all the small orifices with carburetor cleaner, then wipe clean. If you notice any corrosion inside the carburetor or the bowl, you will need a new carburetor. Next, re-install the new emulsion tube and main jet and tighten them down. Install a new metering plug down and re-install the throttle stop screw, and thread in until it sticks out the other side about 1/16 of an inch. Next, install the new spring on the needle valve and snap the new needle valve into the new float. 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 it down. Once rebuilt, re-install the carburetor with a new gasket to seal it to the intake. Re-attach the linkages with the fuel line, and remember to un-pinch the fuel line to allow the fuel to flow again. Reassemble the air filter housing back onto the engine. Once you�ve completed reinstalling the carburetor, it�s time to make the necessary adjustments. Begin by locating both idle screws on the carburetor. One should be marked L (low) and one should be marked H (high). Turn both screws in to shut off fuel, then back off 2 turns. Start the engine, and let it idle for a few minutes. Then, begin turning the L screw clockwise until the engine slows down. Once it has slowed, turn it in the opposite direction until it starts to slow again. Set the L screw at the 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 aluminum-cylinder engines or 1200 RPM for an engine with a cast-iron cylinder sleeve. Now, at full throttle, turn the high speed or main jet screw clockwise until the engine begins to slow. Then, turn the screw back the other way until the engine begins to slow. Finally, turn the screw back to the midpoint. Once adjusted, check the engine�s acceleration by moving the throttle from idle to fast. If tuned correctly, the engine should accelerate smoothly.

The ignition module (or ignition coil) produces the current for the spark plug to ignite the air/fuel mixture inside the combustion chamber. When the magnets pass by on the flywheel, they create an electrical charge, which then travels to the spark plug. To check for a spark, make sure all wires are connected at the module, then hook up a spark plug tester to the spark plug wire and turn the engine over, looking for a spark. If you see no spark, then your ignition module is not functioning. To replace the ignition module, first disconnect the wires going to the spark plug, then remove the bolts securing the module to the engine. Install the new module, hook the wires up, then hand-tighten the bolts to re-secure the module to the engine. To set the gap between the magnets on the flywheel and the module, first insert a business card in between the module and flywheel. Then, spin the flywheel so that the magnets are in the direction of the module, and allow the magnets to pull the module into place. Finally, tighten the bolts down on the module and remove the business card.