The motorcycle jerk, not the one that just split the lanes to speed ahead of you on your drive to work, or the one with the exhaust so loud it rattles the fillings out of your teeth.
No, I’m talking about the strange on-off jerking motion of a motorcycle as it moves down the road which can be quite alarming.
If you have experienced this you know it can be like a bucking bronco trying to get you off its back.
There are a number of reasons for a motorcycle to jerk such as fuel, engine, clutch, drive, electrical issues, and rider error. This is actually one of the biggest complaints motorcycle mechanics run into especially with new motorcycles.
Whether the issue lies in the belly of the fuel system, the depths of the engine, or from parts simply wearing or “breaking in”, this article, will tell you everything you need to know about jerking on a motorcycle.
What is jerking on a motorcycle?
Jerking on a motorcycle is when power from the engine is interrupted intermittently on its path to the rear tire.
This interruption is unusually sporadic, causing power at the rear wheel to transfer to the road, suddenly stop, and then go again, and so on.
This makes the motorcycle “jerk” forward rather abruptly and then stop. Most of the time this happens repeatedly over a short period severely affecting the handling of a motorcycle.
This is known as motorcycle jerking and can be quite concerning when it happens. No wonder it is such a common complaint among motorcycle riders.
Should a motorcycle jerk?
Should a motorcycle jerk? In theory no it should not, however, in practice, every motorcycle will jerk in its lifetime.
This is because a large portion of motorcycle issues deal with how the engine is making power or how this power transfers to the road.
Whether that be something simple like a clutch or chain adjustment to more serious issues such as precursors to transmission or engine damage.
Now that we have established the fact that every motorcycle jerks, let’s look at the causes behind this jerking epidemic.
What causes a motorcycle to jerk?
Motorcycles jerk because power from the engine reaches the rear tire inconsistently, creating moments where engine power to the rear wheel is cut off in some fashion.
A motorcycle can jerk under many circumstances such as during acceleration or deceleration, at constant, low, or high speeds, and even when upshifting or downshifting.
The causes for a motorcycle to jerk can be placed into 5 main categories fuel, engine, clutch, transmission and final drive, and electrical.
Fuel issues that cause motorcycle jerking
Almost any fuel-related issue can cause a motorcycle to jerk because of how vital a constant delivery of fuel is to the smooth operation of the engine.
However, the most common types are low fuel, plugged fuel filters, lines, or passageways, poor gasoline quality, and some things called air and vapor lock.
Motorcycle jerking caused by low fuel
Low fuel in the gas tank is the most common fuel-related issue that causes motorcycle jerking, in carbureted models.
This is because when a motorcycle is in certain positions and the fuel is low it can leave the carburetor without fuel to deliver to the engine.
The fact that most motorcycles lean over while cornering, causes a lot of movement of fuel in the gas tank.
Combine that with the design of most motorcycle fuel tanks that typically saddle over the frame creating two small reservoirs, one of which connects to the carburetor.
You can see it is almost inevitable that once the fuel reaches a certain level in the tank a carbureted motorcycle will start to jerk.
In fuel-injected motorcycles, low fuel-related jerking is all but eliminated mostly because of the constant pressure the fuel pump provides in that system of fuel delivery.
Motorcycle jerking caused by partially plugged fuel lines, filters, or passageways
Partially plugged fuel lines, filters, or passageways are the next most common fuel-related issue to cause jerking in a motorcycle.
The reason is that if a fuel passageway, line, or filter is partially plugged chances are at some point it will become plugged interrupting the fuel flow to the engine.
The passageways I am referring to can be either, holes in a carburetor or holes in a fuel injector, both can be the cause of jerking in a motorcycle.
This highlights how important a constant delivery of fuel to a motorcycle engine is to the delivery of power to the rear wheel and changing this can cause a motorcycle to jerk.
Motorcycle jerking caused by poor gasoline quality
Bad gasoline can cause motorcycle jerking in a process known in the world of engines as detonation.
Detonation, in a nutshell, is when an engine’s fuel burns abruptly before it is supposed to. This means that power delivery to the rear tire will not be consistent.
In fact, this condition will most likely cause more symptoms than jerking most notably an explosion violent enough to send metal fragments through the engine case.
Fresh fuel is vital to the operation of a motorcycle, always add the freshest fuel you can. And no fresh from a fuel storage container doesn’t count if it has been sitting for more than 30 days.
Motorcycle jerking caused be vapor-lock
Vapor-lock can cause a motorcycle to jerk because it affects the flow of fuel to a motorcycle’s engine.
Vapor-lock is when the liquid fuel changes to a gas while still in the fuel delivery system.
This essentially affects the fuel pressure meaning the motorcycle’s fuel supply is not constant, giving rise to a jerking motorcycle.
There is a condition that is confused with vapor lock that happens, especially dual-sport or off-road motorcycles, called air-lock.
Motorcycle jerking caused be air-lock
Air-lock can cause a motorcycle to jerk because it affects the flow of fuel to a motorcycle’s engine.
Air-lock is a restriction or complete stoppage of liquid flow caused by vapor trapped in a high point in a liquid-filled pipe system.
Roughly translated, this means that if a motorcycle’s tank is not venting properly, fuel will not flow to the engine consistently leading to, you guessed it, jerking.
Have you ever tried to pour out a fuel container without opening the vent? Same idea here, a fuel tank has to vent properly or fuel will not come out the bottom end.
Engine issues that cause motorcycle jerking
There are many engine issues that can cause jerking in a motorcycle because this is the workhorse of the motorcycle itself.
Any power delivered to the rear wheel originates from here so if there is an issue here it is only magnified as it is transferred to the wheel.
Some of the most common issues are too much load or stress being placed on the engine, the engine oil itself, or valve issues.
Motorcycle jerking caused by too much load
Motorcycle jerking caused by too much load or stress on the engine is actually the #1 reason why a motorcycle jerks.
The most likely is from not being in the correct gear for your speed or terrain, however, uphill starts and incorrect engagement of the clutch by the rider are also big contributors.
Most of this is from rider inexperience or over-experience (that’s where we get lazy and don’t pay attention) and shouldn’t cause too much damage to the motorcycle itself if it is kept to a minimum.
Motorcycle jerking caused by engine oil
Yes, motorcycle jerking can be caused by engine oil, more specifically, if the wrong type is used or if the oil becomes saturated or contaminated, as it is commonly referred to.
Motorcycles require special oil because the crankcase, clutch, and transmission are housed in the same case.
This means the oils used in motorcycles have special characteristics that lubricate the engine and protect the clutch plates from slipping once engaged.
This brings us to contamination of motorcycle oil, which other than the awesome job it does lubricating, it’s also essentially a bath of everything that enters the engine.
This could be hydrocarbons from combustion that sneak past the rings, moisture from the air, to deterioration from other components.
The bottom line here is, a motorcycle clutch is bathed in oil, if a clutch slips because of this it can cause a motorcycle to jerk.
Motorcycle jerking caused by valve issues
Motorcycle jerking caused by valve issues can usually be traced back to incorrect valve clearance, sticky valve stems, or actual damage to the valve itself.
This would, in turn, affect the compression of the engine which would cause jerking if it happens sporadically.
This is mostly seen in cases where oil on the valve stem has semi-hardened into a paste, causing the valves to stick open or closed at random intervals leading to jerking.
The valves play an important role for the engine as they let in the fuel/air mixture, hold tight for compression, then allow the exhaust to escape.
With this in mind, incorrect valve clearance or small damage to the valve may not immediately cause a motorcycle to jerk but if left long enough the chance is always increasing.
Clutch issues that cause motorcycle jerking
All issues with the clutch, except full failure, will cause a motorcycle to jerk because this is where the transfer of engine power to the transmission occurs.
It accomplishes this task by having steel plates attached to the transmission and fiber plates attached to the engine that when compressed together move the engine and transmission together and when separated move independently from each other.
The causes are improper adjustment, wear or oil contamination, and improper releasing of the clutch lever.
Motorcycle jerking caused by improper clutch adjustment
Motorcycle jerking caused by an improper clutch adjustment is probably the next most common after too much load being put on the engine.
Most of the time it is not the clutch that needs adjustment but the cable or lever that operates them making it an easy fix to motorcycle jerking issues.
A clutch cable or lever that is not adjusted correctly, can lead to a motorcycle jerking, and will need continual adjustment through its lifetime.
Motorcycle jerking caused by wear or oil contamination
A jerking motorcycle can be caused by wear to the clutch steel or friction plates that connect the engine and transmission.
Not only that, a jerking motorcycle can wear the clutch steel and friction plates, which leads to more jerking causing more wear, I think you get the picture.
Oil which is discussed already will not only contribute to motorcycle jerking but will also speed up the wear on the clutch and other engine components starting a circle of its own.
Motorcycle jerking caused by improper clutch engagement
Motorcycle jerking caused by improper clutch engagement is an issue that every rider faces, even experienced riders like myself occasionally release the clutch incorrectly.
Improper releasing of the clutch lever can cause a motorcycle to jerk because if the clutch does not engage properly, the power transfer to the rear wheel will not be constant.
As I have stated before jerking is caused by inconsistent power from the engine reaching the rear wheel.
Transmission and final drive issues that cause motorcycle jerking
A motorcycle chain or belt is a direct connection from the transmission to the tire, making this one of the most likely places a motorcycle jerk will originate from.
In the case of a transmission or a shaft drive motorcycle, jerking could be caused by improperly meshing gears.
Motorcycles can jerk from final drive issues such as incorrect chain or belt tension, or worn sprockets, chain links, or belts.
Motorcycle jerking caused by an incorrect chain or belt tension
Motorcycle jerking caused by an incorrect chain or belt tension is what most people think of when a jerking issue arises.
Due to the rear wheel moving independently from the engine via the rear suspension, the correct tension on the belt or chain that connects the 2 is critical to how smoothly power is transferred.
If a chain or belt is too tight it will cause premature wear or destruction of the chain or belt. If a chain or belt is too loose it will lead to motorcycle jerking along with premature wear or breakage.
Motorcycle jerking caused by a worn chain, belt or sprockets
Jerking on a motorcycle caused by a worn chain, belt, or sprockets is probably one of the most misdiagnosed causes of jerking in a motorcycle.
This is because it is extremely difficult to see if any of these components are worn visually even with another to compare to.
That combined with the fact that chains, belts, and sprockets are fairly large so even a small amount of wear on each sprocket tooth or chain link can add up when you consider the entire length of the component.
Motorcycle jerking caused by shaft drives or transmissions
Motorcycle jerking caused by shaft drives or transmissions is a very difficult one to diagnose.
This is mainly because you cannot visually see these components without tearing them down making it almost impossible to watch them in action.
Gears like those used in a shaft drive or transmission of a motorcycle typically cause jerking due to foreign objects, damaged teeth, or even worn bearings or shafts holding these gears.
Electrical issues that cause motorcycle jerking
Electrical issues that cause motorcycle jerking are very difficult to pin down due to the wide range of influences the electrical system has on a motorcycle.
For instance, the electrical system controls ignition timing which will have a direct effect on how power is created in the engine, whereas a burnt headlight will have no effect on the performance of a motorcycle.
In the end, all electrical issues that cause jerking in a motorcycle are related to the ignition system although some of these causes are from components not normally associated with a motorcycle ignition system.
Motorcycle jerking caused by common ignition components
Motorcycle jerking caused by common ignition components is much easier to track down than some of the more uncommon ones.
Diagnosing electrical issues is difficult due mostly to the fact you can’t really see electricity in action, however, some of the symptoms they cause can be observed.
The main ignition components that cause motorcycle jerking are the stator (the electricity maker), pick-up coil (tells the sparkplug when to spark), the coils (amplifier of voltage), and the sparkplug itself (spark maker)
This is because if any of these components are the cause of the jerking, it will show as a misfire when using a timing light. Along with a multi-meter, locating the issue should hopefully be straightforward.
Motorcycle jerking caused by uncommon ignition components
Motorcycle jerking caused by uncommon ignition components can lead to profanity-laced rants, airborne tools, and grey hairs.
All kidding aside, uncommon ignition components will cause a very similar type of jerking as the common ones because they all interrupt the engine spark in some way.
The problem is locating which one it is. Fortunately, all of the components, with the exception of the ECM or Electronic Contol Module, are tied to safety systems.
These safety systems include items such as the kill or side stand switch and clutch lever, or tip-over sensors.
If your motorcycle is jerking and you notice something unusual with a timing light, the uncommon components are the first items I would look at before even the main ignition ones.
By now you know that anything interrupting engine power from reaching the rear wheel can lead to jerking on a motorcycle, be it fuel, engine, clutch, transmission/final drive, or electrical system related.
Because of this, there are so many reasons that a motorcycle might jerk that you have little option but to break it down into bite-size chunks so that you can narrow down where the issue is coming from.
Hopefully, this information will help you break down and track why your motorcycle jerks.