A well-tuned motorcycle engine is a straightforward machine.
Most bike engines are combustion-powered, meaning they use a system of air, fuel, and ignition to power their pistons and generate momentum.
Therefore, any interference with the air, fuel, or the ignition system will cause a motorcycle to die while accelerating— we’ve broken down the most common reasons for this in the list below.
Table of Contents
1. Worn Ignition System
If a motorcycle ignition system isn’t regularly inspected and maintained, your motorcycle’s ignition spark will weaken until the motorcycle dies while accelerating.
Start by checking the condition of your motorcycle’s spark plugs. As its name implies, the spark plug is the component that sparks the whole ignition process.
Therefore, if your spark plugs are worn, your motorcycle’s whole ignition system is weakened by proxy.
- Spark plugs should be inspected at the service intervals suggested in the owner’s manual by your moto’s manufacturer and if your motorcycle stalls out while throttling.
- Also, inspect the connection between the ignition coil and the spark plug.
- Examine the condition of the ignition leads and the ignition coil.
- Replace any ignition system components if their integrity is compromised, as a weakened ignition system is a common cause of motorcycle stall outs during acceleration.
2. Poorly Adjusted Throttle Bodies
Most modern motorcycles are fuel injected, and those injectors are engineered and tuned to consistently deliver a certain quality of power to your engine cylinders.
If, during routine service maintenance, the throttle bodies aren’t inspected and balanced using a vacuum gauge or via a CPU device connecting to your moto’s ECU, the injectors can go out of sync.
These poorly tuned throttle bodies can cause your motorcycle to die when you hit the throttle.
- There are CPU kits available allowing home mechanics to adjust their own throttle bodies.
- Some skills are required to adjust the throttle besides the vacuum gauge.
- Regardless, we suggest you have a seasoned mechanic perform the adjustment.
- Tampering your injector tuning without adequate tools or knowledge can worsen the adjustment and cause more severe engine failure.
3. Improper Internal Engine Compression
Internal combustion engines require a quality cylinder seal to maintain the power to drive your piston’s momentum.
If the seal between the cylinder bore and the piston rings fails or a gasket is seated poorly, the compression in the engine can escape.
If there isn’t enough compression in your engine, the piston’s movement will fail, and your motorcycle will die under throttle acceleration.
- First, you must locate and isolate the breached seal or gasket to restore the proper compression.
- Replacing these faulty components often requires dismounting and opening up your bike’s engine.
- If the compression is lessened due to damage to the cylinder’s bore, the cylinder may require reboring or the installation of larger pistons and rings.
4. Faulty Ignition Timing
Motorcycle engines comprise various systems of moving parts, all working together.
Therefore, ignition timing is a crucial part of proper engine functioning.
If your ignition timing is early, you’ll experience a dip in engine performance, loud engine knocking sounds from the fuel igniting too early, and interfering with the rotation of the piston. The piston interference can cause the motorcycle to lose power while accelerating.
Adversely, if your ignition timing is delayed, the fuel ignites too late while the piston is already on its way back down the engine cylinder.
Not only will delayed ignition timing cause a noticeable dip in your motor’s fuel efficiency, but it can also cause the bike to die while you’re giving it a throttle.
- On modern bikes, ignition timing is maintained by the motorcycle’s Electronic Control Unit or ECU.
- If an ECU-governed motorcycle is experiencing ignition timing issues, the ECU either needs to be updated or flashed, or the unit itself is faulty and needs to be replaced.
- Older motos stocked a mechanical system of breaker points to regulate their ignition timing.
- These points were synchronized to power the ignition coil at specific times.
- As the point contacts wear down, their timing slowly changes until the bike experiences power loss under acceleration.
- Worn ignition breaker points need to be replaced and tuned adequately to restore your motorcycle’s ignition timing.
5. Clogged Fuel Filter
Suppose your motorcycle’s fuel filter is clogged with debris, moisture, or degraded fuel. In that case, it will fail to transfer energy when you hit the throttle, and the power loss can cause your motorcycle to stall out under acceleration.
While some motorcycles keep external fuel filters, other models have their fuel filters in their gas tanks.
- External filters are easier to replace, while replacing internal tank filters requires removing the entire fuel tank.
- Some riders install external fuel filters that let them bypass the filter located in the fuel tank.
- Regardless of location, a clogged fuel filter is one of the most common causes of a motorcycle engine that dies while accelerating.
Please also read our article about reasons motorcycle dies when slowing down.
6. Jammed Fuel Cap Vent
If you recently took your motorcycle out of storage and now it stalls while accelerating, there may be an issue with the ventilation of your fuel tank due to a blocked fuel cap.
As your motorcycle’s fuel supply heats and repeatedly cools, the vent in your tank’s fuel cap provides a pressure release.
It’s not uncommon for a motorcycle’s fuel cap vent to get clogged with dust, dirt, or debris while in storage for extended periods.
If the motorcycle is ridden before the clogged fuel ap is cleaned out, pressure or vacuum can build up in the tank, hindering the fuel flow and causing symptoms similar to a clogged fuel filter, such as stalling out when you give it throttle.
7. Clogged Air Filter
While the location of the air intake filter varies from make and model moto, all combustion engines require an available air supply for proper acceleration.
If the air filter is blocked by grime and dirt, the air inflow is restricted, causing all sorts of engine running and throttle acceleration issues.
For starters, if the engine’s air intake is obstructed, you’ll notice a weakened or delayed response when you hit the throttle.
Since the air intake is blocked, your bike’s combustion chamber takes in more fuel to compensate—the second symptom you’ll notice on a motorcycle with a clogged air filter is a massive dip in your bike’s fuel efficiency.
Finally, a motorcycle will an obstructed air filter can intermittently die while accelerating until the filter is cleaned or replaced.
- Some motorcycle filters are reusable, meaning you can clean them out with warm water or degreaser, depending on the type and design of the filter.
- Paper filters need to be replaced during routine service maintenance.
- If a clogged air filter is why your motorcycle stalls when you throttle, and you can’t get a replacement paper filter, you can use air to blow out the filter as a temporary solution to get you back on the road.
8. Water in Your Motorcycle’s Fuel Supply
Leaks in your motorcycle’s fuel tanks or compensation build-up over a lengthy period of cold weather storage can make water get into your fuel.
Filling your motorcycle’s fuel tank to the very top before storage can prevent moisture from entering your fuel supply and causing your bike to stall out during acceleration.
- If you suspect your motorcycle has moisture in its fuel supply, empty the tank of all fuel.
- Remove the fuel tank and drain out the fuel lines.
- Blow through the fuel lines and dry them out completely.
- Reinstall the fuel tank and fill it with brand-new, fresh fuel.
- Test ride your motorcycle to ensure it isn’t dying while accelerating.
9. Air-Fuel Mixture Is Running Lean on Fuel
Your bike will lose power if your motorcycle’s fuel supply has more air and less fuel than the motor was engineered to run on.
A lean air-fuel mixture runs hotter than usual, causing improper fuel detonation or pinging.
In addition to motorcycle stalling problems while accelerating, pinging explosions can severely damage your valves and pistons.
The most common reasons for a lean mix are clogged fuel filters and lines or a fuel leak.
10. Fuel System Malfunctions
Modern motorcycle engine operations are regulated by complex engine management systems, typically controlled by the bike’s Electronic Computer Unit or ECU.
If your moto’s ECU detects even the slightest irregularity in your fuel system’s functioning, it will enter the engine into a “limp mode”
A motorcycle’s limp mode hinders the engine’s power to avoid the damage a severe fuel system failure can cause.
If your motorcycle’s ECU detects a problem with the fuel system and enters limp mode, your bike will stall out during acceleration.
While some modern motos have a means of alerting the rider when it enters limp mode, others need to be hooked up to a computer diagnostics unit to read its codes specifying why it restricted engine power.
Here are a few examples of fuel system failures that will trigger the ECU into limp mode and kill your bike’s engine when you hit the throttle.
- Fuel Regulator Failure
- Faulty Fuel Pump
- Pinched or Clogged Fuel Lines