One of the most charming aspects of motorcycle riding is twisting the throttle and feeling the wind rush against you as you accelerate.
But if your motorcycle suddenly loses power or bogs down while accelerating, you’ll likely feel, at best, frustrated and, at worst, like your life is in danger.
This article explains the 12 most common problems resulting in a motorcycle that won’t accelerate.
Here are 12 common problems that often result in motorcycle acceleration problems:
1. Carburetor Spring Is on Backwards
On carbureted motorcycles, the carburetor spring is a small but essential part of the carburetor that controls the carb slide movement and the needle position, affecting air: fuel flow.
If the carburetor spring is installed backward, it can cause the slide to open too slowly or too fast, resulting in a poor air-fuel mixture and a loss of power when accelerating. This usually risks damage to the carb needle and jet.
That said, make sure you read about why a motorcycle dies when accelerating.
To fix this problem, you need to remove the carburetor and check the orientation of the spring. The spring should have a tapered end and a flat end. Also, the tapered end should face the slide, and the flat end should face the cap.
If the spring is on backward, simply remove it, flip it over, and reinstall it correctly. This helps to restore your acceleration and prevent further air: fuel flow issues like backfiring, misfiring, and stalling when you hit the throttle.
2. Vacuum Leak on the Carburetor or Intake Boot
A vacuum leak on the carburetor or intake boot is a hard-to-detect problem that can cause your motorcycle to lose power when accelerating.
A vacuum leak occurs when there is a crack, hole, or loose connection in the hoses or gaskets that seal the air intake system. Air leaks allow extra air to enter the engine, creating a lean air: fuel condition (too much air, not enough fuel), disrupting the air-fuel ratio.
Symptoms of a vacuum leak include rough idle, popping, or backfiring noises, hesitation or stumbling when accelerating, and poor fuel economy.
To fix this problem, you need to locate and seal the source of the leak. Spray water or carb cleaner around the suspected areas and listen for changes in the engine sound while looking for bubbles.
If you find a vacuum leak, you can use silicone sealant, duct tape, or hose clamps as a temporary fix. The most efficient solution is to replace the corroded/damaged/leaking parts.
Related: Motorcycle Idles But Won’t Accelerate? Solved (Explained)
3. Broken Carburetor Spring
A broken carburetor spring may seem like a minor issue, but it eventually manifests some severe problems that can affect your motorcycle’s acceleration.
As we mentioned earlier, the carb spring is responsible for controlling the slide movement and the needle position inside your motorcycle’s carburetor.
If the spring breaks, it can cause the slide to stick or jam, preventing the proper amount of fuel from entering the engine. This could result in the lean fuel condition we described earlier and, eventually, the loss of power when accelerating.
Some of the symptoms of a broken carburetor spring include erratic idle, poor throttle response, hesitation or bogging when accelerating, and engine stalling.
To fix this problem, you need to replace the broken spring with a functional one by removing the carburetor and taking apart the slide assembly.
You should also inspect the carb’s needle and the jet for any damage or wear and replace them if necessary.
Routine carb maintenance should track down weakening springs before they break, restore your acceleration, and prevent further acceleration issues.
4. Plugged Jet in the Carburetor
A plugged jet in the carburetor is a common cause of bogging down a motorcycle’s acceleration. The jet is a tiny passageway allowing fuel to mix with air through the carburetor or fuel injector.
Suppose your motorcycle’s jet gets clogged with dirt, debris, or ethanol. In that case, it can restrict the fuel flow and create a lean air: fuel ratio, providing your engine with too much air and insufficient fuel. This could also result in a loss of power when accelerating.
The symptoms of a plugged jet include rough idle, popping, or backfiring noises, hesitation or stumbling when accelerating, and poor fuel economy.
To fix this problem, you need to clean the jet and remove any obstructions by removing the carburetor and removing the float bowl.
Next, use a screwdriver to unscrew the jet and spray some carb cleaner or compressed air through it. Make sure you can see the cleaner or air coming out the other end.
Finally, reinstall the jet and the carburetor.
5. Extra Slack in the Throttle Cable
The throttle cable is the link between your hand throttle control and the carburetor or fuel injection system. The cable controls how much fuel and air enter the engine when you twist the throttle.
So, if the cable has too much slack, it can cause a delay or a lag in the engine response, making your acceleration feel sluggish or unresponsive. For better insight, make sure you check out our article on why a motorcycle lags when accelerating.
Symptoms of extra slack in the throttle cable include slow or delayed throttle response, difficulty maintaining a steady speed, and poor fuel economy.
To fix this problem, you need to tighten the throttle cable and remove the excess slack by adjusting the nuts or screws on the cable ends near the throttle grip and the carburetor or fuel injection system.
Aim for a small amount of free play in the cable, about 2-3 mm, to improve your acceleration and prevent further throttle response problems from bogging your acceleration down.
6. Exhaust System Restrictions
Exhaust system restrictions can affect a motorcycle’s acceleration by reducing the engine’s power output. The exhaust system allows the burned gases to escape from the combustion chamber and creates a negative pressure that helps draw in fresh air and fuel.
Therefore, if the exhaust system is clogged, damaged, or poorly designed, it can create back pressure that reduces the engine’s efficiency and performance.
Some symptoms of exhaust system restrictions are poor fuel economy, loss of power, rough idle, popping or hissing noises, and excessive heat.
However, you can prevent the problem by:
- Cleaning or replacing the muffler, catalytic converter, or oxygen sensor.
- Checking for leaks or cracks in the pipes.
- Installing a high-performance exhaust system that matches the engine’s specifications.
7. Faulty Timing Advance
An improper timing advance can affect a motorcycle’s acceleration by causing the spark plugs to fire too early or too late in the combustion cycle.
The timing advance determines when the spark plugs ignite the air-fuel mixture in the cylinders. If the timing is off, the engine will not burn the fuel efficiently and will lose power and performance.
Symptoms of bad timing advance include difficulty starting, backfiring, knocking, pinging, or detonation noises, and poor fuel economy.
To fix this problem:
- Adjust the ignition timing with a timing light.
- Replace the spark plugs or wires.
- Check the ignition coil or distributor cap for damage or wear.
- Use the correct octane rating of fuel for the engine.
Bad timing advance can also be caused by a faulty electronic control unit (ECU) or a malfunctioning sensor, such as the crankshaft position sensor or the camshaft position sensor.
8. Air/Fuel Mixture is Inefficient or Dirty
An inefficient or dirty air/fuel mixture can affect a motorcycle’s acceleration by impacting the combustibility of fuel delivered to the engine.
As mentioned earlier, a lean mixture means there is not enough fuel for the amount of air, which can cause the engine to overheat and produce popping sounds on deceleration.
Conversely, a rich mixture means there is too much fuel to the amount of air, which can cause the engine to lose power and produce black smoke.
To inspect and rectify the faulty air: fuel ratio on a carbureted motorcycle, adjust the air/fuel mixture screws on the carburetor to achieve the proper balance for different conditions.
On a fuel-injected bike, connect to the motorcycles ECU with a diagnostics computer and see if the ECU needs to be returned.
Finally, a clean air filter and fresh fuel can also even out an air: fuel mix that’s just slightly off.
9. Dirty or Old Spark Plugs
Spark plugs are essential for igniting the fuel in the engine and initiating the whole combustion process.
If your bike’s spark plugs are dirty, worn out, or damaged, they can’t produce the solid or consistent spark required for engine power, resulting in poor acceleration.
Spark plugs wear out due to everyday wear and tear, poor fuel quality, oil leakage, or carbon buildup. You’ll notice this from signs like hesitation, loss of power, popping sounds, or black smoke.
To fix the problem, you need to clean or replace the spark plugs with the correct type for the engine. You might also want to read about why a motorcycle stutters when accelerating.
10. Clogged Air Filter
Your motorcycle’s air filter is critical for providing clean air to the engine.
If your bike’s filter or air intake cleaner is clogged with dirt or debris, it will restrict the airflow and make the fuel mixture too rich or too lean, resulting in poor acceleration.
This can happen due to riding in dusty or muddy conditions, neglecting regular maintenance, or using the wrong or cheap filter.
Some of the symptoms of a clogged air filter include difficulty starting, rough idle, or reduced fuel economy.
Some motorcycles stock reusable mesh air filters that can be degreased, cleaned out, dried, and reused, while others use disposable paper filers. Note that disposable paper filters need to be changed per the service intervals in your bike’s owner’s manual.
To fix your bike’s acceleration issue, your air filter may need to be cleaned or replaced with a new one.
11. Fuel Delivery Issues
Fuel delivery failure can affect a motorcycle’s acceleration by preventing enough fuel from reaching the engine.
Faulty fuel delivery often results from a clogged fuel filter, a defective fuel pump, a pinched fuel line, or contaminated fuel. Symptoms include hesitation, stalling, backfiring, or reduced power.
To restore proper fuel flow to your motorcycle and bring its throttle response back to where it should be, inspect and clean your fuel delivery system as needed.
Next, fill your bike with fresh gasoline, draining any expired or contaminated fuel that might be sitting in your tank and lines.
It’s Time To Clean Your Carburetor
Carburetor contamination can affect a motorcycle’s acceleration by creating an improper air-fuel mixture. This is due to the accumulating presence of dirt, gum, or varnish deposits in the carburetor passages and jets.
The build-up of debris inside your bike’s carb is often responsible for a broken carburetor spring or an incorrect adjustment of the carburetor screws and other carb issues covered elsewhere in this article.
Here are a few of the signs indicating that it’s time to inspect, clean, or rebuild your motorcycle carburetor:
- Rough idling.
- RPM surging
- Exhaust popping
- Thick or black exhaust smoke.
Usually, the first step to restoring the acceleration on a carburated motorcycle is cleaning and adjusting the motorcycle’s carburetor according to the manufacturer’s specifications, following the service manual instructions.