A motorcycle stall-out is more than just embarrassing; it can be hazardous.
The joy of motorcycling is the harmony maintained between mind and machine, knowing that where you look, the bike glides…
When you stall out, you’re not going anywhere. So, to prevent our readers and riders from being a sitting duck on a bike at an intersection, we’ve compiled a list of reasons motorcycles stall.
Table of Contents
1. Rider Input
The most common reason for motorcycles to keep stalling out is improper clutch input at the rider’s hands.
An engine stalls out when the rear wheel isn’t receiving enough power from the engine to propel the bike forward.
Stalling can happen due to various causes, the most common being the rider failing to engage the clutch while decelerating the throttle during stops or shifts.
How to Ride a Motorcycle Without Stalling
Here’s how to prevent a motorcycle from stalling while riding:
- Start the bike and put it in neutral. With the motor running, ease onto the front brake to steady the bike.
- Keep your right foot down to steady the bike. Pull in the clutch with your left hand and use your left foot to downshift from neutral into first gear.
- Now switch feet. Stand on your left foot, put your right foot on the rear brake pedal, and use your now free right hand to throttle up gradually.
- While the revs climb, slowly release the clutch lever to engage your motorcycle’s clutch. You’re looking for the friction zone, where the clutch grabs and power loads the motor.
- Once you’re in the friction zone, the bike will start to “power walk” itself forward. Pick up your feet, release the clutch the rest of the way, and throttle up until you’re in motion.
Consult your owner’s manual for the rev matches for each gear. To shift without stalling, repeat that process in motion, with your feet up, of course.
2. Motorcycle Sat Unmaintained for Extended Period
If a motorcycle sits stagnant without being prepped for storage, corrosion and rust can cause it to keep stalling out.
The fuel, oil, seal, gaskets, and lines of a bike that’s sat unkempt for a long while will start to corrode and build-up clogs, affecting the bike’s air and fuel circulation.
I will get more into the specific details of each component, but a bike that’s been sitting tends to stall unexpectedly both at stops and during shifts.
You can prevent this from happening by riding your bike at least once a week, prepping it properly, and winterizing it before long bouts of storage.
When you take your bike out of storage, give its tank, motor, transmission, and lines a thorough inspection, then update the brake fluids, motor oil, fuel, and air filter.
Also read our article on 5 Reasons Motorcycles Misfire When Hot Or Cold
3. Improperly Tuned Air-Fuel Ratio
A motorcycle with a poorly set air-fuel ratio has the potential to keep stalling out while riding.
Just like lighting a fire, firing up that motorcycle engine requires three ingredients:
Your bike motor was engineered with a combustion chamber that functions off of a specific ratio of air to fuel. And combustion doesn’t just happen during ignition. It happens every time you hit the throttle.
It’s combustion that explodes out of your pipes and propels your bike forward, and if your bike is running either too lean or too rich on fuel, you might stall out every time you hit the throttle.
But if your bike’s ratio is off and too much fuel enters the chamber, it’ll flood your ignition process. And if it’s too lean, there won’t be enough fuel to ignite, and the airflow will extinguish your combustion.
You can remedy this by re-tuning your carb, or on fuel-injected bikes, by having the mechanics re-flash your bike’s CPU fuel maps.
4. Excess Throttle Cable Play
Your throttle cable can fall out of adjustment, slacking itself loose than it needs to be for accurate throttle response, and this can cause your motorcycle to stall out during acceleration while riding.
The throttle cable connects to your carburetor on a carb bike and opens the butterfly valve according to the rider’s input.
On a fuel-injected bike, it signals your CPU you inject the appropriate amount of fuel.
Either way, the more you throttle, the more air-fuel mixture is pumped into the combustion chamber.
On a carb bike, if you have too much slack in your throttle cable, you won’t have enough tension to open the butterfly valve, and the air-fuel ratio will be off, causing the bike to lose power while accelerating, sometimes even to stall out.
Rectify this situation by inspecting your butterfly valves with the bike off and see if they’re opening fully when you blip back the throttle.
If they’re opening in unison with the motion of the throttle, valves fully opened when the throttle is fully engaged, your throttle cable might have some extra slack.
This may be something you can adjust yourself using the tightening nut that attaches the throttle cable to the carb.
If you’re having trouble tightening it to the point of no slack, your cable might be old, worn, and stretched out, and you may need a fresh throttle cable replacement.
5. Bad Timing Advance
Bad timing advance setting on a fuel-injected motorcycle can delay spark plug timing, which could cause your engine to lose power and stall out during acceleration.
Engine timing functions to regulate the ignition coil spark with the motorcycle’s speed; low speed, low sparks, high speed, high sparks.
If your engine timing is off, your spark plug fires out of sync, and much like the slacked throttle cable mentioned above, when you hit the throttle, your bike could actually lose power. If it’s bad enough, your bike could stall out.
If the timing is bad, your power loss might be accompanied by backfiring as well.
Poor timing could result from a worn or damaged mechanical timing cam, or it might result from an electrical issue.
If you bought your fuel-injected bike used, find out if it has any after-market power enhancements. Whoever installed them may have messed with your engine timing.
Self-fixing bad motorcycle timing is something I’ve never done, nor do I plan to. It’s a complex job that, if done wrong, could cause some major, hard-to-reverse problem to your bike.
If you’re experiencing power loss during acceleration, with or without stall outs, especially if it’s accompanied by backfiring, take your motorcycle to a tech who specializes in your brand and have the professionals reset your timing for you. For them, it’s an easy fix.
6. Vacuum Leak
A vacuum leak in your intake manifolds allows an increase of air in the combustion chambers’ air-fuel ratio. If a motorcycle’s air-fuel ratio is off, your motorcycle will have running issues that may lead to stalling.
Inspect the intake boots on the bike’s carb. Time and corrosion can crack these boots. These cracks can leak, so replace them as needed.
Also, check the quick-release hose clamps around the intake boots. If they’re not fastened all the way, they could be letting air in. If they’re loose, tighten them, clamps down.
Next, examine the carb gaskets. The gaskets on the carburetor can crack over time just like the intake boots, and just like with the boots; a crack becomes a leak in no time. If your carb gaskets are cracked, replace them with some fresh ones.
7. Broken or Jammed Carburetor Spring
A broken carb spring won’t open the butterfly valve when the throttle is twisted, causing the bike to run rich and lose power during acceleration, which may cause the motorcycle to stall out.
If you’re beginning to feel like an improper air-fuel ratio has become a reoccurring theme in this piece, you’re not wrong. As mentioned earlier, running rich is when a motorcycle’s air-fuel ratio has too much fuel and not enough air. A bad air-fuel mixture will cause your motorcycle to lose power or kill your ignition completely and make the bike stall.
If you think you have a broken carb spring, inspect your butterfly throttle when the bike is off and see if it’s opening when you twist the throttle. If not, pop that carb off and swap out your broken carb spring for a crisp new one.
Please make sure you put it on the right, though; we use a backward carb spring that can kill your bike’s power so bad we’ve dedicated the whole next section of this article to it.
8. Carburetor Spring Installed Backwards
If the carburetor spring is incorrectly re-assembled after rebuilding or cleaning a carb, it will cause acceleration issues to make the motorcycle stall out.
A carb spring that’s been assembled backward will function backward, doing the opposite of what you want it to do.
On a healthy and functional motorcycle, yanking on the throttle tugs the throttle cable and opens up the butterfly valve to push air into the carburetor for combustion. A backward carb spring, on the other hand, will push that butterfly valve shut.
If that valve is closed, the air isn’t getting into your combustion chamber, causing a loss of power that might make a motorcycle stall.
To rectify this problem, disassemble the backward carb spring that connects to the throttle cable, flip it around, and reinstall it properly.
A handy home mechanic might be able to do this with the carb still mounted onto the bike, but it’s easier to take the carb off before uninstalling and reinstalling the spring.
Once it’s all hooked back up, with the bike still off, twist the throttle and see if the valve opens and closes in unison with the throttle.
9. Clogged Carb Jets in the Carburetor
If debris or bad gas clogs your jets, your motorcycle will lose power during acceleration and stall out. Clogged jets mean your fuel can’t transport to the combustion process, and your air-fuel ratio will run lean.
As we’ve outlined numerous times above, an improper air-fuel ratio can make a motorcycle stall.
If you’ve got clogged jets and have been experiencing power loss during acceleration that sometimes causes the bike to stall out, pop the carb out of the motor. Spray it down with carb cleaner and give it a thorough cleaning to relieve any clogs or debris build-up that will affect fuel flow.
Carb cleaning is part of routine maintenance on a carbureted motorcycle. Keeping up with the general carb service is an effective way to keep your motorcycle from stalling.