Learn How to Troubleshoot a Small Engine

Few things are more frustrating than when your small engine won't start or runs rough. Before you call it quits and bring the machine to a service shop, there are some basic troubleshooting steps you can take.

Video Transcript

Welcome back to the RuggedMade Tech Corner. I'm Jared. Today we're going to be talking about troubleshooting your engine. Your RuggedMade log splitter probably came with a Raven engine like this or a Honda GX engine like that but you're probably familiar with most of these engines from Kohler, Briggs, Harbor Freight Predator. There's a Honda GC motor. They go in machines like snow blowers and lawn mowers, generators, and construction equipment such as plate compactors. A common question we get asked is, "How do I troubleshoot an engine that isn't running right?" Maybe it won't start or it's hard starting. Maybe it won't rev up. Maybe it sputters and dies. If it has an electric start, maybe the electric start isn't working. So, these are some common problems and the most common causes of these issues is bad fuel and lack of maintenance. Now, lack of maintenance really isn't a problem with the engine. We'll put that under operator error but some parts can wear out and parts do fail.

In today's video, we're going to go over some standard troubleshooting steps that should help you identify what the issue is. Now, depending on what that issue is, it might be a pretty easy repair that you could do at home with basic tools. Some of the issues could require more work, some replacement parts, and you may feel more comfortable bringing your machine to a local small engine repair shop, but either way, let's go over some of the basics and see if we can get the engine running right.

Before we talk about troubleshooting, have you been keeping up with your routine maintenance? I'm talking about oil changes, air filters, and on engines with a lot of hours, valve adjustments. If you haven't been doing that, break out that owner's manual and get caught up on the routine maintenance first and you might find that that takes care of whatever issue you are having. Typical maintenance tasks should be done on a regular basis based on hours of operation and, in some cases, on condition of the environment in which you run your engine can also affect how often some of these service tasks need to be conducted. Getting an hour meter can be a handy way to help you keep track of that maintenance schedule. You should check the overall condition of your engine on a regular basis, basically every time you go to fire it up, especially if you haven't run it for a while. Give it a once over looking for things like leaks, damage, loose bolts, mouse nests, things like that.

Let's talk for a minute about safety. Most of these troubleshooting steps are easy and safe; however, these are engines. They do run on good old gasoline, which is very flammable, particularly the fumes. So, if you're draining or adding fuel, do that in a well-ventilated place, preferably outside. You don't want those fumes accumulating. And, keep spark-like flames and cigarettes, things like that, away from the fuel. Don't run the engine in an enclosed space like a garage or a shed. Do that in a well-ventilated place so that you don't have the risk of carbon monoxide poisoning. There is a small shock hazard from the spark plug and the ignition coil. And, you want to use caution when you're connecting and disconnecting your battery. You don't want to create a spark or damage your electrical system. And, keep in mind, once your engine's been running for a while, that muffler will get nice and toasty on a hydraulic log splitter.

If your engine seems to be completely locked up and you cannot pull the pull-start rope at all, make sure the directional control valve is in neutral. If the valve has one of these detents for the return position and the spool was left in that position, the hydraulic system will be locked up and blocked. Sometimes, the engine happens to run out of gas just as the rod was retracting. This prevents the pump from turning which locks up the engine's crankshaft. Some folks are in the habit of shutting off the engine at the end of the day just as the rod is still retracting and that's going to set you up for failure the next time you go to start it.

The most common cause of hard starting and rough running in an engine is bad gas. The gasoline that you buy at your local gas station is what's called E10, which means it has 10% ethanol or ethyl alcohol. Ethanol is derived from sources like sugar cane, corn, and wheat. The problem is ethanol can cause problems, especially in smaller engines like this that sit around a lot. Think about your snow blower in the summer, your lawnmower in the winter, you get the idea. So, ethanol can cause corrosion in metal parts but it also can cause problems with things like your fuel line, gaskets, and seals, things like that. If you've ever worked on an old snowmobile or a jet ski or an old car, maybe you've seen the results because there was a time when ethanol was new and cars and engines were manufactured out of components that weren't really ethanol-proof. Fortunately, nowadays, engines are manufactured with basically ethanol-resistant components so that's really not a problem anymore.

The biggest problem with ethanol is that it attracts water when exposed to air and, as you can imagine, water and fuel - they really don't mix well. So, that fuel can in your shed may seem like it's airtight but there could be a leak. If it has an air vent, maybe you didn't tighten that last time you used it and if it's half full, there's still a lot of air in there containing moisture and the exposed walls on the inside of the tank provide a place for water condensation to form. E10 gasoline can only absorb so much water. If an excessive amount of water is absorbed into the fuel, something called “phase separation” will occur. This is where the water in the fuel will separate out and sink to the bottom of your fuel can or your gas tank and from there it gets sucked right into your carburetor. Gas can absorb an excessive amount of water in as little as two weeks, so to reduce the chances of water getting into your engine, use fresh fuel and store it carefully. A can that's been sitting in your garage for more than 30 days could already be stale or contaminated and treating it with a stabilizer like this as soon as you get back from the gas station can also help keep the fuel fresh longer; however, most experts seem to agree that no stabilizer can make stale or gas that's already phase-separated usable again. The best method is to use ethanol-free fuel. This kind of fuel can be found at hardware stores and lawn and garden dealerships, usually in these one-quart and one-gallon cans. But, if you know what this stuff costs, you know that it can get pretty pricey. If you're lucky, you may have a gas station nearby that sells these five-gallon pails. So, this is a pretty good way to buy ethanol-free fuel; however, even in five-gallon pails it doesn't really make financial sense to run something as large as a snow blower or a generator or a log splitter on ethanol-free gas. These are anywhere from 5 to 15 horsepower engines. With smaller engines, like on a chainsaw or a trimmer, if you're not running it all day every day like a commercial user, ethanol-free fuel can be a relatively cost-effective way to do it. It's typically high-quality fuel and you know that every time you go to start that engine or that chainsaw, it's probably going to fire right up. Where we recommend using ethanol-free fuel even on these bigger engines, like on your log splitter, is for storage and we'll come back to the storage topic later in this video.

If you're having a hard time getting your engine started and you suspect bad fuel, drain all of the fuel out of the fuel tank, the fuel lines, and the carburetor bowl. Then add fresh fuel from a reliable source. Use ethanol-free fuel, if at all possible, because this is going to remove the possibility of bad fuel from the equation and it should simplify the troubleshooting process. If the engine starts and runs properly, well, you know that fuel was the issue.

Engines need fuel, air, compression, and spark to run. So, let's start with making sure that the engine is getting fuel. There's a fuel line here and a kinked or blocked fuel line can prevent the fuel from getting from the tank to the carburetor. If the fuel tank vent is not working, you can also get a vacuum that will prevent the fuel from flowing down to the carb as well.

Now, a tricky symptom to diagnose is when the engine starts and it runs but after about 30 seconds or so it dies out. Now, sometimes, a partially kinked fuel line or that vacuum-lock effect can prevent fuel from flowing down to the carb at a sufficient rate. It is dribbling down in there but it's just not enough for it to run and so after a few minutes it accumulates in the bowl. That's enough to get the engine started but then after it's burned off the fuel that's in the bowl, it dies out. So, turn off the fuel petcock and we're going to remove the drain bolt on the bottom of the carb bowl. It's this one here that's at an angle and it takes a 10mm socket and you probably want something to catch any fuel that might be in there. Now, turn on the fuel petcock and check to see if there's sufficient fuel flow. So, if there's sufficient fuel flow to the carburetor now, you can reinstall this bolt. And, turn your fuel petcock back on.

A stuck float inside the carburetor can also block fuel. Sometimes a light tap on the bowl of the carb with the plastic handle of a screwdriver is enough to free that float. Carburetors can also get clogged internally. These have very small ports and passageways inside that can easily become clogged. Just look at the size of the hole in the main jet. This is for a 420CC engine. It's still tiny. So, if any of these holes become restricted or clogged, you're going to have a hard time getting the engine to run right. So, you're going to need to remove the carburetor and either rebuild it, clean it, or replace it. To prevent this from happening, make sure that the fuel filter (which is located on the bottom of the tank) is clean and there's also a fuel strainer up here on the top of the tank. You want to make sure that this is clean and that it's in the tank so that debris can't get in there.

Flooding is more related to how to start the engine but it can cause hard starting too. Cranking the engine with the electric starter or the pull starter causes fuel to be introduced into the carburetor. It's mixed with air and then this fuel-air mixture travels into the combustion chamber. Excessive cranking without the engine running can cause a flooded condition. Having the choke on causes a richer air-fuel mixture and that can mean even more fuel’s being pulled into the engine. So, the engine can get locked up with this raw fuel. If the engine locks up, immediately stop attempting to start it. There could be excessive liquid fuel inside the combustion chamber and that doesn't compress. If you suspect the engine is flooded, remove the spark plug. Most engines come with a spark plug wrench like this, and the standard NGK BPR6ES Spark Plug takes a 13/16” socket. To remove the spark plug, we're going to pull off the spark plug boot and then use our socket. Now we're going to use the pull starter to turn over the engine so even if you have electric start, don't use that, and don't have your face near the spark plug hole in case there is raw fuel in there because it's going to squirt out. If fuel comes out, the engine is definitely flooded. Keep pulling it over until no more fuel comes out. Then, let it sit in a dry, well-ventilated place for a few hours to dry out. Put a clean cloth over the spark plug hole so that nothing can fall inside. And, also allow that spark plug to dry out or replace it with a new one. Reinstall the spark plug being careful not to over tighten it these threads are very fine and it doesn't require much torque. And now, reconnect the spark plug boot and try starting the engine.

These engines can flood while being transported, so they must be properly prepared first. When I say transporting, I'm talking about both towing in the case of say, a log splitter, and carrying it in the bed of a truck, in the case of, say, a generator or something like that. The point is road vibration can cause the float in the carburetor, which is this little guy, to flop up and down. That's going to allow raw fuel to enter the engine's combustion chamber. If the engine was running, that fuel would be burned but since the engine is not running, it becomes flooded and that makes it difficult to start. So, the fuel can also dribble down into the crankcase where it can contaminate the engine oil. Operating your engine with engine oil that's been contaminated with fuel is going to cause serious damage. It can be tough to determine whether there's fuel in the oil. You may be able to detect the smell of fuel or you may… the oil may feel kind of thin on your fingers. If you suspect there is fuel in the oil, just replace it. A quart or two of engine oil is cheap insurance and you're probably overdue for an oil change anyway, right?

So, what should you do before transporting a machine? Just run the engine with the fuel petcock in the off position until the engine stops. It's going to sputter out and die by itself. That will burn off most of the fuel in the bowl and it'll also prevent additional fuel from the fuel tank from flowing down into the carb.

Most lawn and garden engines are equipped with a low-oil cutoff switch like this, and it's located here on the side of the crankcase. If the oil level is low, this switch will stop the engine to protect it from damage. It does this by grounding out the ignition coil which kills the spark. You always want to check your oil level when the engine is cold. So, you remove your dipstick. And, even though there's a dipstick, the oil level should actually come right up to the top of the threads of the fill port. Just because there's some oil on the dipstick, doesn't mean there's enough oil for the engine to run safely. Note that operating on a slope can trick the low-oil sensor into thinking that there's insufficient oil, so always check the oil on a level surface. If your engine or splitter is tilted like this on a slope, the oil could slosh away from the sensor and that's why it thinks there's not enough oil. And, this is one of the reasons that most people remove or bypass the low-oil switch when they install this type of engine on something like a go-kart. So, if the oil level is correct but the engine will not start, you can bypass the low-oil sensor to test if the sensor itself is faulty. The wiring can vary from engine to engine so this technique, it's a little beyond the scope of today's video. The sensors, they're quite reliable, anyway. Making sure the engine has enough oil is usually sufficient for troubleshooting purposes and you should do that anyway to avoid damaging the engine. But, these sensors do fail once in a while so keep an eye out for a future tech video showing how to bypass them. Honda recommends SAE 10w30 conventional oil for general, three-season use. 30-weight conventional oil is also suitable for typical, three-season use in mild climates. For cold weather operation, you can get winter or snowblower 5W30 conventional oil or sometimes that's 5W30 synthetic. 5W30 synthetic is pretty much ideal for year-round use except in extreme, low-temperature conditions when you may need to do things like preheat the oil outside of the engine and then pour it in, or you could just stay inside.

A clogged air filter will reduce airflow to the carburetor causing the engine to run rich. A severely clogged air filter can prevent the engine from running completely, so you need to replace the air filter element periodically. Some foam air filters like this, they can be cleaned a couple of times with gentle soap and warm water between replacements. Just refer to your owner's manual. So, here we've got a few common examples of engines. Here on the Raven, it's this foam type of air filter. We've got a little Honda GC190 here, which uses this paper element, sort of a waffle, and then on the standard Honda GX-type, you've probably all seen these types of filters.

The environment in which you operate your engine will affect how much maintenance it needs. The air filter on a log splitter that's being run in your backyard will usually not clog up quickly. A plate compactor being used on a dusty job site, on the other hand, can end up with a severely clogged air filter in no time. Mice also love to turn the air filter housing into a mouse house so check to see if any of the little guys have moved in. I like to keep a couple of these around my splitter, my snowmobiles, [and] in the shed just in case. The spark plug, the spark plug boot and wire, the ignition coil, the ignition switch, this one is for a pull-start engine and this one's for an electric-start engine, are all possible areas of failure and that low oil cutoff switch is also part of the ignition circuit. So, remove the spark plug and check the condition of the electrode. If it's black with carbon or if it's wet, install a new one. The Raven and the Honda GX series engines use an NGK BRP60s which is also called a 4008 but refer to your engine's owner's manual for the correct spark plug. Reconnect the spark plug to the spark plug boot and lay the spark plug on the engine so that the electrode is close to a metal part of the engine. Now, make sure you can see it or you could position a camera or your cell phone and record it and look at it after. Turn the ignition switch to the ON position. Now, being careful not to get shocked, you're going to pull the engine over or you could use the electric start. If you see sparks, the ignition system is okay. If there's no spark, the ignition system is going to require further diagnosis. So, stay tuned for a video where we go into more detail on how to do that.

The valve gap or valve latch must be inspected periodically and adjusted as necessary. As the engine breaks in, the valve gap can change. So, here we've got the valves on a GX390 and they have some play because we checked them with a gap gauge. If the gap is too tight, the valves will not fully close and this causes low compression. That can make the engine hard to start and hard to keep running. It can also reduce the amount of power that the engine can generate. So, if any of the steps that we've covered above don't resolve a hard starting or stalling issue with your engine, check the valve gap. Refer to your owner's manual for the inspection interval and check out this video on how to adjust the valves.

All of these engines come with [a] pull start. If your engine has [an] electric start and it's not working but you can start the engine with a pull starter and it runs normally, well, the problem is probably within the electric start system. The most common symptom of a problem with the electric start is you hear a click when you go to turn the key and the engine doesn't turn over. This usually indicates that your battery is weak. Use a voltmeter or a multimeter like this to check the condition of the battery. It should be at least 12.6 volts at a resting state. Don't try to evaluate the health of your battery by measuring the voltage right after you disconnect it from a charger. Anything lower than 12.6 volts means you should charge your battery or replace it. We recommend a smart charger, something like a battery tender or an OptiMate. These maintenance chargers are great. They'll give it a full charge and keep it charged. They also won't overcharge it, so they can be left connected to the battery. Some may even have additional functions like a desulfate mode.

There are other tools you can use to determine the condition of your battery. For example, this is a load tester. Or, you can bring it to your local auto parts store where they will probably test it for free. Remember that batteries lose a lot of their cranking capacity in cold weather, so one thing you can do in the winter is bring it inside to warm up before using it. We don't recommend jump starting on [a] battery this size from a big car battery or at least if you do that, don't have the car running at the same time. A small jump pack can be helpful, too.

The electric start panel will either have a circuit breaker, like this one, or an internal fuse. Reset the circuit breaker if it trips. Replace the fuse if it blows. If the circuit breaker continues to pop every time you try to start the engine or if you keep blowing fuses, check the wiring on the battery. The polarity could be backwards. Also, check that the connections are tight to the battery to the ground on the engine block and to the positive terminal on the starter relay. If the electric start system still doesn't work, the problem may be in the electric starter itself or the starter solenoid, or it could be in the wiring. We'll cover these repairs in a separate video.

If your machine is not going to be used for two or more weeks it should be stored properly to prevent starting problems the next time you go to run it. If you've been running pump gas, drain all that fuel from the tank and the carburetor bowl. Now, option one is to store the machine in this dry condition. If you get it bone dry and if you live in a dry climate, this method should be fine. Option two is to fill the tank 95% full and leave an extra 5% for expansion. Most engine manufacturers recommend this method for storage. It reduces the chances of water getting absorbed into the fuel and it should prevent rust on your tank. We highly recommend using, of course, ethanol-free fuel for storage. It's pretty easy to find these days so there's really no reason not to. If ethanol-free fuel is not available near you, you can add fuel stabilizer to fresh pump fuel, but be sure to follow the instructions on the bottle. Don't exceed that ounces-per-gallon ratio. For example, this stabilizer is only one ounce for 10 gallons. Now, run the engine for a few minutes to make sure that you're ethanol-free or your treated fuel has had a chance to work its way through the carburetor, shut off the fuel petcock, and now your engine should be ready to go the next time.

I hope you find this tech video helpful. If you stay on top of your routine maintenance, I'm confident you'll find these engines are very reliable. Stay tuned for more tech videos where we'll do a deeper dive into some of these diagnostic techniques, the routine maintenance, and the repairs that will help you keep your engine in tip-top shape. Thanks for watching.