ATVs are thrilling to ride, but not when it’s going through the symptoms of low compression. You want to go out and race through the woods, jump some sand dunes, or get to your perfect hunting spot, instead, your ATV is choking and sputtering. This isn’t the day you planned.
Symptoms of low compression in your ATV include misfiring, sputtering, clouds of blue or white smoke, and overall poor performance. You may have to add oil constantly, or your weekend ride won’t even start at all. Some problems can be fixed even if you’re not a mechanic with a garage full of specialty tools, while others will require that specific knowledge.
If you’re here searching for these answers and more, we have you covered. Here we will go over the symptoms of an ATV that has low compression, how to diagnose them, and what options you have to get it fixed. Keep on reading to find out how to get back out and have fun on your ATV.
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How Do I Know if my ATV has Low Compression?
One of the most common symptoms your ATV has low compression is loss of power. Misfiring is another symptom. You may also see white smoke, strange noises, and extreme vibrations, or you may not even be able to start it. The following symptoms will help you diagnose whether you have a compression issue with your ATV.
- Misfiring Engine—When the cylinders aren’t working properly you end up with a misfire. It could be a bad mixture of gas and air, or it could be because the valves aren’t seating properly. Engine misfire usually feels like a rough idle, you hear strange sounds, or you just know something is “off” with the engine.
- Leaking Oil—You may find a thin film of oil around the engine or on the spark plugs. You might also notice that your oil level drops faster than it should but you don’t see any drips or oil puddles under the ATV.
- Rough Running—When your ATV rattles so much you have to tighten bolts and screws as you’re riding, you may have an engine with low compression. If the clutch engages on its own while the ATV is in use, it means the idle is too high, which is a possible ATV transmission issue. Engines do vibrate, but they shouldn’t rattle your teeth or be uncomfortable.
- Won’t Start—When the engine turns and turns but it never “catches,” you could have a compression issue.
- Blue or White Smoke Trail—A very faint and thin trail of white smoke isn’t necessarily a bad thing, as it’s usually just vapor burning off. But if you see a medium or heavy amount of white smoke you are probably burning oil. When you see blue smoke, you know the ATV is burning a lot of oil.
Burning oil is a sign of low compression. It’s usually because of a bad head gasket or worn piston rings, both keep oil where it belongs. Oil shouldn’t be burning in the compression cylinder.
- Plug Fouling—Spark plugs do wear down over time and need to be replaced occasionally. When they foul out you have a compression issue somewhere. If you pull the plug out for an inspection and it’s covered in oil, or it smells strongly of gas, then there’s something amiss with your engine.
- Oil Level Prematurely Low—Some oil consumption is normal. Oil gets very hot and some is burned off during normal uses. It’s normal to have to add a little oil here and there.
Over time you know how much oil gets used through typical riding and you know you have to add some occasionally in between oil changes. But if you have to add oil every time you ride it, but you don’t see any outward oil leaks then you have a compression issue in your ATV.
Confirming Your ATV has Low Compression
The way you can check your ATVs compression is by using a compression gauge. It’s a round gauge that looks similar to a speedometer, but it has a short rubber hose sticking out of it, and it should have metal threads at the end.
You screw the end into the spark plug socket, and when you turn the engine over, the gauge shows you how much compression is being created in the engine’s cylinder.
You can purchase a compression gauge online or at most automotive parts stores. They range from about $20 to $100 and are worth the cost if you’re a do-it-yourselfer. When you’re having engine problems with your ATV, a compression gauge will help you narrow down the issues.
When your engine is misfiring, it could be something as simple as a clogged fuel filter, or spark plug. The problem could also lie somewhere internally. Unfortunately, you probably won’t know unless you’re able to check the compression.
Now that we know how to check for low compression and what the symptoms are, let’s see what the causes are.
Causes of Low Compression
Valves in your ATVs engine allow the fuel and air mixture into the cylinder, then release the spent mixture out the exhaust pipe. When they malfunction, you can get low compression issues.
Valves can break, get excessive buildup on them, become worn down, or a valve spring can break. Each of these issues keeps the valve from sealing well, or opening and closing when it should. These issues lead to significant engine complications that will need to be addressed by a well-qualified mechanic.
The next issue, unfortunately, isn’t an easy fix either.
Blown Head Gasket
A bad or leaking head gasket can cause a lot of performance issues. The head gasket sits between the engine cylinder and the engine block and keeps oil, coolant, dirt, and air out. They are subjected to extreme heat and pressure and will eventually weaken and fail.
Symptoms of a failing head gasket include white smoke coming from the exhaust, engine overheating, loss of compression, coolant in the oil, or vice versa. When oil and coolant mix you might find a milky or muddy-looking substance coating the dipstick.
While some weekend mechanics may be able to replace a head gasket, unless you have done this job without issue many times before, we suggest taking it to a mechanic. All it takes is a tiny imperfection, or a slight nick in the gasket to end up with the same problem again.
This next cause of low compression is a cheap and easy fix that most people can manage easily.
When you’re getting good compression readings of your compression gauge, but the motor won’t start, you could have a bad spark plug. Remove your spark plugs, check them, and replace them if the contacts are worn down, cracked, or they are covered in soot.
You should also check your plug wires for cracks, splits, or corrosion on the contacts and replace them as needed.
Worn Piston Rings
Piston rings prevent excess oil from entering the combustion chamber, help to carry heat away from the piston head, and build up compression. When they go bad they can cause a myriad of symptoms, including low compression.
Over time, even the best cared for engines will have piston rings wear down. High-performance ATV engines may experience worn piston rings sooner than your average ATV.
Fouled spark plugs, too much oil in the combustion cylinder, and blue exhaust smoke are all symptoms of worn piston rings. You’ll need very specific tools and have a lot of engine know-how to replace piston rings. This job should only be attempted by trained professionals, so if you suspect this problem, take your 4-wheeler to the mechanic.
While many compression issues are very difficult to fix, some are straightforward like our next entry on the list.
Clogged Fuel Filter
Grit, dirt, and other debris can get into the fuel, so combustion engines are usually fitted with fuel filters. Over time, like all other filters, the fuel filter will get clogged and need to be replaced.
Low compression can be caused by a clogged fuel filter. When the combustion chamber doesn’t get enough fuel, you can experience low power, a sluggish engine, and trouble accelerating.
Since ATVs are usually flying full speed in some of the dirtiest places, many riders replace their fuel filters at the same time they replace the air and oil filters. If you haven’t replaced your fuel filter in some time, you might want to do that to see if it fixes your compression issue.
While you’re checking fuel lines, go ahead and check the gas in the tank.
Gas can go bad from sitting for long periods. Even when you pump fresh gas into your ATV, it could have water or impurities in it, especially if the holding tanks are cracked. So check the fuel if your ATV is having compression issues.
If you see anything floating in the fuel, or you see water in the tank, drain it out and replace it with clean fuel. When you’re going to put it away for the season, it’s a good idea to drain the fuel or add a fuel stabilizer so you don’t have trouble when you go to start it again.
You bought your ATV to go riding, not to spend time taking it apart in the garage. Unfortunately, an issue such as low compression will keep you from getting out there and tearing up the trails. Low compression can be either an easy fix or one that will require the professional touch of a trained mechanic.
Causes of low compression include bad gas, a clogged fuel line, broken or bad spark plugs, worn piston rings, a failing head gasket, or valve issues. The first three causes can probably be repaired in your own garage, while the last complications will need to be repaired by a qualified technician.
We hope this article has helped you figure out why your ATV has low compression and has helped you get the problem fixed. We’ll see you next time on the trail! Happy riding.
I’m William Guzenski, ASE certified master automobile technician & automotive expert. I love to attend race events and car shows throughout the country. I also loves to travel 40-foot motorhome, exploring abandoned mines and ghost towns. I’m currently building another car for Bonneville Salt Flats and will be campaigning a drag car at several events.