Five Reasons Your Motorcycle is Sputtering

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It can be extremely frustrating when your motorcycle has problems that prevent you from being able to ride it. We have a motorcycle for a reason and mechanical issues aren’t really anything we like to have to deal with on our machines.

A few mechanical problems on motorcycles can be expected, especially if they are older models. I’ve owned a lot of motorcycles the past few years and have run into every mechanical issue possible. Sputtering issues were a common problem I faced.

What causes a motorcycle’s sputtering? There are many reasons why your motorcycle might stop working. Most common causes are problems with the carburetor, such as a fuel leak or vacuum leak. You could also be experiencing corroded spark plugs, cracked spark plug wires, an ignition coil problem, clogged filters, and engine timing problems.

To ignite a motorcycle’s combustion chamber, you will need fuel, air, and spark. Examining the mechanics that deal with these three components will ensure you’ll find your sputtering issue. I’ll discuss the most common reasons for sputtering.

Sputtering Due To Carburetor Issues

Carburetors were a great mechanical product to help older machines. They are capable of providing the proper air and fuel mixture that the engine requires to run the motorcycle. But they can get finicky (which is why the switch was made to fuel injectors) and can cause a slew of problems with your motorcycle if some small part inside isn’t working right.

If you have a carbureted motorcycle that is sputtering, you’re likely culprit is the carburetor. Three main problems can occur with the carburetor and your bike will sputter. The first problem is a vacuum leak. The second is a leak of gas. And the third is that your carburetor needs tuning. These repairs can be made easier if you have the right tools. Click here for my recommendations.

First, we’ll discuss the possibility of a vacuum leak within your carburetor. Vacuum leaks can cause many issues, particularly sputtering. If there’s a vacuum leak, that means the carburetor isn’t giving the proper amount of air to the air and fuel mixture which will ultimately result in sputtering and poor engine performance.

Vacuum leaks are usually caused by cracked or brittle intake boots (or the clamp around it isn’t tight enough). This is between the engine and carburetor. If you suspect that this is the problem, your intake boots can be easily replaced.

Unplugged vacuum ports can also cause vacuum leaks in carburetors. Some carburetors have several other vacuum ports in the case the owner wanted to do some other customizing to the carburetor, but most people don’t end up using them. The vacuum port plugs are inexpensive and easy to install.

Gas leaks from the carburetor will make the motorbike sputter. A cracked or brittle gasket at the bottom of a carburetor can cause leaks. This is usually the culprit. You will smell gas and be able visually to see any leaks. You can also read our article on other reasons why your motorcycle may leak gas.

Also, float bowl gaskets can be inexpensive. A tutorial online will show you how to replace your float bowl gasket. If you have more than one carburetor, it’s a good idea to change all the float bowl gaskets because they’re probably worn out too.

Sputtering can also be caused by a third issue with the carburetor. If a carburetor is not in adjustment, it means that the air/fuel screw or balance between carburetors (if more than one) must be adjusted.

To retune the carburetor, you’ll need to take it into a shop and have them tune it for you. It is usually around $50 and they have all the tools necessary to do it quickly and easily.

A video series I created about motorcycle restoration includes a 25-minute video detailing how to clean and rebuild carbs. The series also covers other difficult-to-tackle parts such as electrical and body work. I give dozens of tips and tricks that you won’t find anywhere else online. Click here for more information if you’re interested in viewing multiple videos that will help fix up your bike or if you’re interested in completely building your dream motorcycle!

Sputtering due to Ignition Problems

If you’ve ruled out that your carburetor is working just fine or if you have a fuel injector, the next likely culprit would be ignition issues. Ignition problems could be caused by three things. The first is the ignition coil. Second, the sparkplug wires. Third, the sparkplug(s).

First, check the spark plugs. Make sure you take out the spark plugs. Also make sure the point isn’t worn down and that the gap between the center and the ground electrode is the appropriate distance. Online you can find the exact gap for your spark plugs. The tool is available at any auto shop.

A malfunctioning spark plug will cause the cylinder it’s connected with to misfire which will ultimately cause performance issues and the motorcycle to sputter.

Next, inspect the spark plug wires. An issue that is common with older motorcycles is the section of the sparkplug wiring that connects to it; this connection head can sometimes be threaded on to spark plug wire. The threaded connection can corrode and rust over time.

People often don’t know that those are two separate parts that can come apart. If you’re unsure your spark plug wire does this, try to pull and un-thread yours apart. If it’s pretty snug on there, it’s probably not threaded and likely not the problem. If it does appear to be threaded you can clean it up, snip it, and rethread the connection head on the spark plug wire.

Also, check for cracks in the spark plug wires. If there are any cracks anywhere on the wires, the spark will arc to your motorcycle frame because that’s the path of least resistance for the electricity and it won’t arc through the spark plug. This will cause the cylinder not to fire if there is no electricity to it. You’ll simply need to get a new spark plug wire.

The ignition coil is another possible cause of sputtering. The ignition coil may not send enough spark to spark plugs, which can again lead to misfires in the engine.

This is the most likely scenario with an ignition problem. If you suspect that the ignition is the problem, it is best to have this checked by a mechanic. Ignition coils have really high voltage and is dangerous to handle if you don’t know exactly what you’re doing with it.

Clogged Air Filter Can Cause Sputtering

Another possible cause of sputtering is a clogged motorcycle air filter. An clogged or dirty air filter can cause the engine to not get the proper amount of air in the fuel mixture.

It is important to replace your air filter regularly. People forget about them until they have problems. If you have an older motorcycle, the air filter can be found on the side of your engine. It is worth checking to see if it is dirty. Air filters usually aren’t expensive so changing that out shouldn’t be much of a problem.

If you have pod filters, examine them to make sure there isn’t some sort of residue on them that’s preventing air from flowing through them. You can click here to read our article on pod filters vs. air boxes.

Sputtering because of timing issues

A motorcycle can sputter from timing problems, though it is rare. It’s pretty hard to have the timing randomly start getting off by itself and is usually caused by either someone rebuilding the engine and getting the timing off or someone tried to fix the timing themselves previously.

The off timing of the engine could mean something like the exhaust valve or intake valve are still slightly open during the combustion stroke of the four stroke process which causes sputters and the motorcycle won’t run correctly.

A mechanic is the best way to diagnose timing issues on a motorcycle. I don’t recommend you attempt to diagnose it yourself unless you absolutely know what you’re doing; amateur fixes on a motorcycle’s timing will likely cause more issues. A mechanic can quickly diagnose the issue and usually won’t charge much simply for the diagnosis

Similar Questions

How can you make a motorcycle run smoothly? Check the motorcycle’s air/fuel ratio to fix it running rich. Also check for stuck floats and clean the carburetor. For more information, click here.

Is it possible for a carburetor or fuel injector to be converted? It is possible to change from a carburetor or fuel injector. You will need to have some mechanical skills and knowledge about electric wiring in order to convert a carburetor into a fuel injector.

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