Motorcycle Dies After Revving: 9 Most Common Reasons & Fixes
Here’s the scenario: It’s your usual weekday morning and you are looking to use your bike for the day. It might just be a quick stroll or you might need to get to work in about an hour. You get to your bike and remove the cover. You get on to the seat and press the starter. You hear a good start-up sound and the engine seems to catch. It idles for a few moments, then you squeeze the throttle and engine revs up. However, it suddenly goes down and dies. You try it again, it’s the same thing.
There are two things that are included in this scenario:
- It could possibly be a temporary problem that goes away later in the day. But then it does happen regularly. So, it still is a problem.
- It happens all the time, every time, rendering your motorcycle unusable.
Possible causes and fixes:
Assuming that you are already out on the street and upon squeezing the throttle, it suddenly feels like it is running out of gas. It sputters and eventually, your engine goes dead. Well, naturally you would have to pull your bike on the side of the road for safety.
Cause #1: Choke lever left open (for older models)
A choke is a valve cable that restricts the flow of air to your carb. It allows your engine to temporarily run rich, so it could fire up and run even when the engine is cold. What happens is, the air is restricted and more gasoline is pushed into the chamber, making it run lean.
How to use the choke: Fully open your choke then start your engine. Rev halfway just enough for your engine to catch idle. And once you get a steady idle, kick it into gear and run for 1 or 2 minutes. Close the choke then rev your engine and ride as usual.
The problem occurs when you might have forgotten to slip back your choke lever to the “off” position, and you have been running for quite some time already, This eventually floods your carb and as a result, your engine sputters and dies no matter how you gun it.
Do not forget to put back your choke lever to “off” position as soon as your engine is warm. Some riders just simply turn off their choke position to “off” when their engines catch idle. However, these may differ with the climate, some engines stay cold longer while tropical climates may afford shorter warm-up times. You as a resident and a rider can adjust accordingly.
Conversely, newer EFI bikes have a fast idle lever in place of a choke. It helps the idle go faster on cold morning starts. You use it only if you have problems with the idle. Otherwise, your engine should be good once you start with these newer bikes.
Cause #2: Petcock Lever is not on “On” Position (For Older Motorcycles)
If you are riding an older classic bike, chances are it has a petcock lever that has three settings. “Prime”, “off”, and “on”. A petcock lever is a main valve fuel entry control that is connected to the combustion chamber.
- Prime: Lets fuel run freely even with the engine not running. It is mainly used when you have vacuum leak problems
- On: It only lets fuel run to the carb if the engine is running and there is a vacuum
- Off: It simply turns off the valve like a faucet.
Put Petcock lever to “On” position and then test your engine.
Cause #3: Air to Fuel Ratio Running Lean (carb type)
When your carburetor is “running lean” it means that there is too much air against gasoline in the mix. When there is a lack of fuel, even when you fully open your throttle, your engine dies since there is little or no fuel being fed to the carb. The result? An engine stall.
The first step is to assume that you may still have the right amount of air coming in, and not to touch the air screw just yet. And, the first thing you need to do is make an adjustment on the fuel screw. Turning it clockwise goes to lean, and turning it counter-clockwise goes to rich.
So, by doing a quarter turn one at a time going to rich, you may observe how the idle goes. If you can hear some improvement on the idle by just doing this. Go ahead and test your throttle. If your engine no longer dies, then your problem is solved.
If the problem persists, you can try to make a complete adjustment of your air to fuel ratio system. You will need a tachometer for this and if you don’t have one then you can go by ear. However, if you are exacting when it comes to measurements, you can go instead to your nearest OEM service center for recommended carb settings. On the other hand, If you are a veteran rider then this is a perfect opportunity for you to practice your Air-to- Fuel ratio balancing skills.
Cause #4: Clogged Fuel Filter
Normally, a fuel filter would look clear, and the dark part of it should have liquid in it. And it should be working.
Pull out the fuel filter and blow air through it. If air passes through, then the filter is good. If not, it’s clogged. Install a replacement fuel filter and test ride your bike.
Cause #5: Defective Fuel pump
Among all other symptoms of fuel pump failure is the loss of power.
You can try this: Locate your fuel pump inside the fuel tank. Physically reach down and put a finger on it, click the ignition switch from “off” to “on”. If you can hear it click once, it is working properly, as it is priming itself. If it doesn’t click check your fuses. If you can hear it clicking several times or more than four times, it is likely that it is going bad or broken. You need to replace it.
Cause #6: Idle Too Low
When a motorcycle idle is too low, there isn’t enough opening for the air and fuel to pass through when your engine is in action. With an unusually low idle your motorcycle is near its choke point wherein any command from the throttle could easily kill the rpm.
Recommended RPM for idling: (use a tachometer)
1200-1500 for single-cylinder motorcycle
1000- 1200-and above- for 2 cylinder engines
Cause #7: Clogged Fuel Jets (carb)
There are two jets in your carburetor: The main jet and the pilot jet. Most of the time if any dirt gets into any one of them, it is likely that the pilot jet is the one that gets stuffed since it is a lot narrower. And apart from the loss of power when revved, it can also cause a lot of other problems which are directly related to what we are tackling in this article.
Remove carb then open to detach jets. Please refer to the manual for disassembly and reassembly. If you are a novice, but willing to learn and have some time go ahead and remove. If not, it’s always wise to refer to your expert mechanic. Once jets are removed, check and peep through the holes against the light and see if there are any dirt or debris trapped. Clean out the jets with air pressure then wash with gasoline to remove any remaining grime. Reattach jets and reassemble carb. Reattach carb and run your bike.
Cause #8: Colder Climate
So this one is pretty much self-explanatory. You might live in a state where it is colder than most, so it takes more time for your engine to heat up and catch on for it to be stable enough.
Follow the procedure for using choke (refer to cause no.1) Allow more time than usual for the engine to warm up before gunning the throttle or leaving the house. Avoid storing your motorcycle where ice can form and cling to it. It could form condensation that could possibly go into your fuel tank tainting your gasoline. Tainted fuel is much harder to burn. The key is to be patient and listen to your engine.
Does Your Motorcycle Die After it Warms Up?
This scenario, if not directly related to the main title of this article, is something very similar to our main topic. So, any of the fixes you see in this article are relevant to this issue. Hence, you can use the same tips and fixes to solve the problem as mentioned above. Moreover, there are some additional suggestions to fix this problem.
The reason why this question differs is that when your motorcycle is already warmed up and it stalls, you can already discount issues about cold starting or cold weather. This one is definitely internal. Let’s add a list to of possible fixes for a stalling warm engine:
- Air to Fuel Ratio is lean- refer to cause #3
- Clogged fuel filter- refer to cause #4
- Idle too low- refer to cause #6
Cause #8: Intake leaks
Intake leak is what happens when a rubber “boot” that connects the carburetor head or injector unit to the cylinder head. Over time this “boot” is subjected to heat, fuel, and other corrosive elements. This then could possibly crack and degrade this rubber “boot”. A crack or hole can then cause a vacuum leak that in turn causes the engine to have an irregular idle, and ultimately lose power due to air leaks.
Replace intake boots. Confirm fix by testing engine when warm.
Cause #9: Low Compression
Low compression on a motorcycle engine could mean a myriad of problems inside the engine block. It could be worn out piston and rings, the valves or even a cracked head.
This is a major concern that only a qualified technician can handle. Otherwise, if you are a veteran of motorcycle troubleshooting you can always refer to your manual for exact specifications.
Play hard, ride well.