Like all combustion engines, the power of a motorcycle is generated by the smooth functioning of its ignition, fuel and air intake systems.
Therefore, if there’s a hiccup with the ignition spark, timing, fuel supply, or airflow, the motorcycle’s power supply and throttle response will drag.
This article elaborates on the most common problems that cause a motorcycle to lose power at high RPM. It also explains how to restore the engine power of your bike to where it should be.
1. The Ignition System Is Faulty
One of the most common reasons a motorcycle loses power at high RPMs is worn spark plugs, ignition leads, or ignition coil. Ensure you inspect, maintain, and replace the critical ignition system components during routine service intervals.
If you notice failure in your ignition system, consider the following:
- Using the service manual for your motorcycle’s make and year model, start by inspecting your spark plugs for signs of scorching, ordinary wear, or discoloration. Ensure you replace them at the first sign of wear to keep your bike from losing rev-power.
- Examine your ignition leads next, as they can incur corrosion from riding in harsh conditions or improper storage. This is often in addition to the wear and tear they experience through the combustion process and rapid changes in engine temperature.
- The ignition coil is another critical yet often overlooked component that causes your motorcycle to lag at high RPMs once it’s worn out from engine heat and repeat ignition.
2. Your Fuel Filter Is Obstructed
If your motorcycle’s fuel filter is stuck with carbon fuel deposits, water, corrosion, or grime, it prevents the appropriate amount of fuel from reaching the combustion chamber. As a result, your motorcycle will lose power during RPM boosts.
- When you attempt to rev your motorcycle into the higher RPM range, it injects more fuel and air into the combustion chamber to provide extra power.
- If the fuel filter is clogged, the combustion chamber fills with air while the fuel struggles to get past the filter. This causes an improper air-to-fuel ratio.
- The inadequate fuel supply translates to a power loss, especially when attempting to throttle up the higher rev range.
Before you can inspect and clean a fuel filter, you may need to drain and dismount the fuel tank.
That said, replacement fuel filters are cheap and replacing a faulty fuel filter is easy once you’ve got the tank off. If the filter is clogged, we suggest replacing it rather than struggling to clean it.
If the filter is clogged with corrosion or rust particles, inspect the inside of the emptied fuel tank and the fuel lines to be sure they aren’t the source.
Make sure to also check why a motorcycle won’t start after running out of gas.
3. The Fuel Injectors Are Clogged
Modern motorcycles use computerized fuel injection systems to inject a precise fuel amount into the combustion chamber at an exact time. If a bike’s fuel injector is clogged, the motorcycle will lose power when you hit the throttle and attempt to inject fuel to boost your RPMs.
These injectors have microscopic openings that can get clogged by grime, rust, or fuel contaminants that were either formed in the lines or passed through the fuel filter.
Clogged injectors are especially common on motorcycles with ripped or missing fuel filters.
If the injectors are caused by debris, you can clean it by flushing your bike’s fuel system with an injector cleaner. The cleaner is usually an additive you can mix in your fuel tank. For the best results, we suggest following the instructions provided by the cleaner manufacturer.
Furthermore, you can prevent your motorcycle from losing power under acceleration by:
- Only using high-grade, manufacturer-recommended fuel.
- Inspecting and replacing your fuel filter based on the service schedule outlined in your owner’s manual.
4. Your Bike’s Carburator Jets Are Blocked
Vintage motorcycles used mechanically operated carburetors for air (fuel delivery) rather than computerized injection systems. The bike will, therefore, lag at high RPMs if the carburetor jets are blocked with debris, corrosion, or fuel grime.
- Unblocking your carb jets requires removing, cleaning, and rebuilding your carburetor.
- Although a carb rebuild isn’t the most complicated procedure, it must be rebuilt perfectly to restore your bike to full power up through the rev range.
- Clogged carbs can be avoided via routine inspection, proper fuel filter maintenance, and only running high-quality, high-octane fuel through your motorcycle’s fuel line.
Also check our article on why a motorcycle dies when the choke is turned off.
5. The Air Intake System Is Leaking
If your airflow is losing pressure due to a leak somewhere in your air intake system, your motorcycle will lose power at high revs due to a loss of air pressure, engine compression, or a lack of air in the fuel ratio.
Furthermore, an internal air leak can allow air into your fuel lines, causing the mix to lean on fuel for combustion. This makes the engine performance to lag, especially under acceleration.
Mind you, since air leaks can happen because of a faulty seal, gasket, hose, line, or pipe, diagnosing it can be complex without professional equipment.
6. The Air Filter May Be Blocked
The air intake filter is typically a part of the air box unit, devised to filter dust, debris, and moisture out of the air supply. This filter sucks air in through the air box and feeds it to your combustion chamber.
Just as it is with a fuel obstruction, any hindrance to the airflow can result in a skewed air-fuel ratio, which hurts your motorcycle’s rev power, especially when attempting to climb up the RPM range.
You’ll likely notice your motorcycle is using more fuel than usual, despite having less acceleration power. This is because less airflow allows more fuel to enter the combustion chamber in place of the missing air.
An air-fuel ratio that’s short on air and rich in fuel can cause delayed engine timing and a slow rev response. You’ll experience this most especially when hitting the throttle hard to raise your RPMs quickly.
If your motorcycle loses power at high RPMs when you rev up quickly but makes it slowly up the range when you handle the throttle lightly, cleaning your air filter could be the solution.
- Some air filters are reusable. These are mostly filters made of foam or metal mesh that can be cleaned, dried, lubricated, and reinstalled to help your bike power up like it’s new.
- Other bikes use disposable paper air filters that must be thrown away and replaced when they become faulty. This helps to keep them from making your motorcycle throttle to drag at hard, fast revs.
7. The Bike May Be Experiencing Delayed or Advanced Ignition Timing
If the ignition timing of your motorcycle is thrown off and the bike advances or delays from its precise timing sequence, combustion can happen either early or late in the pistons cycle. This will also make the motorcycle to lose power at high RPM.
Advanced ignition timing can cause the engine to knock, as the fuel ignites before the piston cycles. The explosion impedes the piston’s motion, which can cause a motorcycle to die before it can rev up.
Adversely, the delayed ignition timing can flood your cylinder with fuel that should’ve been combusted, wasting gas and energy in a counterproductive way to your engine power. It could also stop your bike from reaching its full RPM potential.
Please, also check why a motorcycle won’t idle after throttle.
- The ignition timing on fuel-injected bikes is regulated by an Electronic Computer Unit (ECU) that controls the fuel injection process.
- These ECUs require periodic updates to keep the engine tuned and the ignition sequence operating at the ideal time.
- If the ECU is damaged and the unit flashing doesn’t fix it, the ECU itself may be the reason your motorcycle loses power before it hits high RPMs.
As for vintage motorcycles, they use a mechanical points system to manage their engine timing.
- The points are tuned to ignite the ignition coil at a specific tempo.
- As the tips of the points wear down from use, tiny variations in the points cause changes in that tuning.
- Even the slightest shift in the size of the point can cause enough of a tempo change to delay or advance the motorcycle’s ignition timing. This may also make the motorcycle to lose power before it reaches high speeds.
8. The Fuel System May Be Faulty
To prevent engine damage or a dangerous accident caused by severe fuel system failures, the ECU on modern fuel injected motorcycles often comes programmed with a limp mode.
The ECU communicates with a network of sensors dispersed throughout your fuel and ignition systems that relay data back to the ECU.
If one of the sensors reports a critical failure, or if the ECU loses contact with one of the sensors because of damaged wires or sensor failure, the motorcycle enters the limp mode. In this state, the engine power of your motorcycle is restricted to prevent irreparable damage or a crash.
While some motorcycle’s ECUs enter limp mode due to a failure within the fuel system, the ECU will prevent the bike from powering up to the higher RPMs for safety’s sake.
You should also learn about why a motorcycle won’t rev past 4000 – 6000 RPM.
In some cases, the sensor will need to be replaced in order to restore the bike to full power.
That said, some bikes will stay in Limp Mode even after the issue has been rectified. In this case, it is until the ECU is plugged and flashed by a diagnostics machine at your local dealership that the issue gets resolved.
The following problems can result in an ECU limp mode limiting your bike’s power:
- Faulty Fuel Pump
- Fuel Regulator Failure
- Faulty Fuel Filter Failure
- Faulty or Erratic Fuel System Sensor
6 reasons your motorcycle is losing power when accelerating | MotorcycleHabit