Most Harley bikes stock air-cooled V-Twins powered, regardless of the year model.
While these are simple, combustion-based machines, issues with air, fuel, or spark can cause false starts and engine stalling on any HD model.
This article lists the most common reasons a Harley-Davidson motorcycle keeps stalling.
Table of Contents
1. Air/Vacuum Leak
Suppose your Harley-Davidson develops a vacuum leak in its air intake system. In that case, the air-fuel mixture starts to run rich, the engine loses compression, and your Harley will experience frequent stall outs, especially after the bike is warmed up and running.
- Like all carburetors, HD carbs require constant inspection, detailed cleaning, and replacements to avoid air leaks that lead to engine sputtering and frequent stalling.
- Vacuum leaks often develop due to a dried-out and cracked-open air intake boots or a faulty gasket or seal.
- On older, carbureted Harleys, vacuum leaks commonly form around worn-out carb seals that need to be replaced.
Here’s an example of a conversation between two real-life Harley owners explaining the symptoms and the cause:
“I haven’t ridden my 2010 ultra classic for about a month due to the weather here. It has half tank of gas in it, as it shows I still ride another 100 miles before filling up. So this weekend was warm enough to ride, start the bike, idle for a few minutes, then head out and fill it up, in first gear while am turning to the gas station, it was stalling like it wants to die….–“
“–Sounds like intake leak if it wants to stall after warm up.”
Once the air is escaping your intake system, the fuel fills the space left in your combustion chamber by the air loss. The change in the air/fuel ratio has a negative impact on your Harley’s combustion/piston action.
Furthermore, suppose your Harley’s air vacuum is severe enough. In that case, so much fuel is allowed into the chamber that your HD’s ignition system can’t burn it all.
The excess fuel can flow into your exhaust system, causing backfiring, sputtering, and a Harley-Davidson that shuts off while riding.
And finally, an air leak anywhere in your Harley’s intake system allows the air to escape before it reaches your combustion chamber and lets the airflow reach areas where it doesn’t belong, causing running issues, idling issues, and stall outs.
2. Clogged Fuel Tank Filter/Fuel Injectors
Suppose your Harley’s fuel tank filter is blocked by coagulated fuel, moisture, dirt, or corrosion from your tank walls. In that case, your motorcycle will keep stalling due to the lean air/fuel ratio caused by the impaired fuel flow.
“I have a 2012 [Harley-Davidson] Road King police model with 14k on the clock. My fuel pump regulator just recently crapped out and left me stranded on the side of the road… I also found my fuel filter was approximately half to three-quarters clogged.”
On a Fuel Injected Harley model, clogged fuel injectors produce the same symptoms.
Fuel injectors are the part that sprays fuel for combustion. At the same time, the filter is meant to filter out fuel contaminants before they enter the lines.
Therefore, if your HD has clogged fuel injectors, your filter may be faulty too.
Either way, a blocked filter and clogged injectors can cause your HD’s fuel supply to run lean.
Conversely to the rich fuel mix described in the previous section, a lean air/fuel mix allows too much air into your combustion chamber, which can cause a noticeable decline in engine power, wavering RPM revs while riding, engine overheating, no starts and shuts off whilst riding.
“I have an 09 [Harley-Davidson] Road King, and the other day, at low speed, the thing started spitting and sputtering, and then it quit. I started it back up, but it would just spit and sputter and then stall. So far, I have replaced the sparkplugs and ensured the electronic control module (ECM) was correctly connected.
That sounds like a fuel problem. 2009s are fuel injected, if my memory serves me. It could be:
- Clogged fuel filter.
- Bad gas – water in the gas.
- Clogged injectors
- Failing fuel pump.
- Failing fuel pressure regulator.
If the gas looks good, I will try to run some Seafoam through it. You can add it directly through the intake as well as put it in the gas tank.”
Unless you are a decent motorcycle mechanic, you may have to take your bike to a Harley-Davidson dealership to check the filter, fuel pump, or fuel pressure regulator.
3. Faulty Cam Chain Tensioner
While some of the older Harley-Davidson motorcycles used cam gears to keep engine timing, HD now equips all their motorcycle models with cam chains.
These cam chains often have tensioners to adjust them in real-time as they run, as metal chains expand from the heat of motion.
Suppose a Harley-Davidson motorcycle’s cam chain tensioner goes out. In that case, the cam chain slacks itself looser than spec, and your HD’s engine timing is thrown off in the process. Once the engine timing is faulty, your Harley’s engine will perform erratically, make clanging noises, and keep stalling.
“2014 [Harley-Davidson] Street Glide was running perfectly, quiet, no issues. Stopped at a set of lights and suddenly rough idle, clattering noise from the primary case, stalling. It runs badly, like a diesel engine, and will rev between 1200 to below 900 and eventually stall. On start-up, will rev to 1800-2000rpm… Initially, NO CODES were thrown. After installing the new CHT Sensor, it throws P0505, loss of idle speed control. [The problem] turned out to be a bad primary cam chain tensioner.”
4. Faulty Cam Position Sensor
Modern Harleys have electronic fuel injection systems controlled by electronic computer units (ECU).
This ECU is also responsible for governing a modern Harley’s ignition timing, air intake, and fuel flow.
Your ECU communicates with a network of sensors that monitor your bike’s engine conditions, adjusting the ignition timing and air/fuel flow accordingly.
Many modern Harley models have the cam position sensor, which relays the angle of your cam or crankshaft to the ECU.
The ECU then adjusts your ignition timing to account for the angular shift.
Suppose the ECU, the cam position sensor, or the connection between the two is compromised. In that case, the ECU may change the ignition timing without proper cause.
The cam position sensor on many Harley-Davidsons wears out from moisture damage or electrical failure, such as frayed wiring. If the cam position sensor is faulty, your HD will start OK but stall out while riding.
“My other half has a 08 HD DYNA Low Rider, and we cannot figure out what is wrong with it. After it warms up, it will cut out, backfire, and just die a lot while riding down the road–
–Engine backfiring and stalling after it gets warm is a symptom of a failing cam position sensor (ignition pickup). Behind the round cover on the cam case.”
“My 2001 [Harley-Davidson] Road King (fuel injected) will run just fine for about 3-4 mi. Then it loses spark and dies. I let it sit for 10 -15 min., and it starts right up. It will go another 2-3 mi., and same thing it will die. I put a new coil on it and didn’t change anything. The second time it happened, I tried to restart it right away. Nothing. So I checked for a spark. Nothing. Five min. Later I checked for a spark again, and it started off the arc on the screwdriver—two mi. Down the road, the same thing happened, no spark. All the other electrics are working fine when this happens to the spark. I put a new crank sensor on it, and it’s running like a bear!”
5. Clogged Air Cleaner
All Harley-Davidsons require air filters that clean the dirt, dust, and moisture out of the air supply as it enters your HD’s intake system.
While some Harleys are out there with reusable air cleaners that can be de-greased and reinstalled, many HD cruisers use disposable paper air filters that need to be replaced per the spec outlined in the owner’s manual.
Failure to keep up with your Harley-Davidson’s air cleaner can result in a clogged filter or intake manifold, cutting off your bike’s air supply.
Clogged air intake causes your fuel mix to run rich on fuel, much like if you have an air leak. The result is misfiring, backfiring, poor engine performance, and a Harley that starts fine but stalls out while riding.
“[I let my] 2010 [Harley-Davidson] ultra classic [sit] for about a month due to weather… I filled up gas and went for a 40 miles ride, while I was riding, it was stalling all the way and scared the hell of me… I take her back to the garage, thinking maybe the battery needs to be charged, I check the battery, and if it is charging, it is full, and it is charged… it was running well before, and it started fine as usual just when riding that it stalls.
If the battery starts the bike, it is not the reason the engine stalls at idle. You may have a dirty IAC (Intake Air Controller). They get gummed up and will cause stalling, especially on a warm engine.”
6. Ignition System Failure
One of the most common reasons a Harley-Davidson motorcycle keeps stalling is because of failures within the ignition system. Your HD’s ignition system includes the spark plugs, their wires, and your ignition coils and leads.
“1988 Harley-Davidson FXR. was driving battery shorted out. It blew the headlight and taillight bulbs out, and the bike died. Please put in a new battery and change the bulbs, but they have no spark. Changed coil, and still nothing–
I would check the coil first and see if it needs to be replaced. If it’s new and you still have a receipt, take and get a replacement coil for the one you bought and make sure your wires coming out of everything have power by tracing the system to see if there might be something short.”
Inspecting your ignition system components, maintaining your coils, and changing your spark plugs are parts of routine maintenance on any motorcycle and are one surefire way to keep your Harley from stalling out.
7. Compromised Battery Terminal Connection
One of the most common issues causing Harley-Davidson motorcycles to stall out is so simple it often gets missed; loose or rusted battery terminal connections can cause an HD to stall out while riding.
It’s no secret that HD cruisers have some of the market’s loudest and most heavy-vibrating stories. Riders often find the bike their Harley starts up just fine but then keeps stalling and shutting off when in motion.
Once the bike’s RPMs rise, the engine shakes, rattling the already loose terminals and causing power loss, sputtering, and stalling.
In other cases, corrosion interferes with the terminal connection.
A good detail scrubbing is all it takes to stop your HD from shutting off while you ride.
Regardless, you’d be surprised how many capable home Harley mechanics pull apart their air, fuel, and ignition systems in search of a problem, only to find out it was just a loose battery connection.
“My bike is a [Harley-Davidson] 98 Dyna Super Glide evo engine. The bike runs great for about 45 minutes, then stalls start right up, and you can continue riding. Replaced coil, keyed ignition, and ignition module.
Someone suggested replacing the cam position sensor—”
“–It’s not the cam position sensor [because there’s] no such thing on an Evo.”
“I bought a new 2022 road glide special, and it started stalling out on me while I was going on the highway today happened two times.”
“I had an issue with stalling and jerking about a month ago. It ended up being battery ground cables. Always check your battery cables and grounds when it comes to stalling and sputtering intermittently—at least, that’s what I’ve learned.”
We suggest a quick battery inspection on your Harley at least once a month, before and after long rides, track riding, off-roading, or riding through harsh weather.