Does your motorcycle stall while riding or when you twist the throttle? Or can you get going down the road, then it cuts out? On top of it being really annoying, it can be very dangerous for your motorcycle to stall out when you are going down the road. I use to have this problem and I was able to figure out the issue with some digging. Most of the Stalling problems usually deal with the carbs not working correctly. Hopefully this article will be able to point you in the right direction to get your motorcycle working and learn what I did to get my bike fixed.
When does it Fail?
The First thing you need to figure out is HOW or WHEN the motorcycle stalls out. The more information you have about the problem, the better chance you have on figuring out a answer. For example, saying “My motorcycle stalls” is not very helpful for a technician or Google search. The problem, it’s to general of the description. Now if you were to say “My motorcycle stalls when riding down the street” it is more helpful and can narrow down the issue. With this description I will know that the bike is warmed up and it is not a simple issue. (This is the problem I had with my 1984 Nighthawk)
The first thing you need to figure out if the carburetors are dirty or not jetted correctly. Most stalling issues have to deal with the carbs not working correctly or efficiently. If the carbs are clogged with bad gas it will not allow enough fuel to fix with air to run the motor.
If the carbs are in a elevation that it is not setup for, it will also cause problems. Fuel injection can figure out how much gas to add based on the sensors throughout the system. Carbs do not have that ability. The air is thinner the higher you go up and carbs are a mechanical system. That means it will always add the same amount of fuel no matter how thick or thin the air is. If you believe this is your issue, you can buy new jets to replace the ones you have installed. Just make sure you get the right kind for your motorcycle.
Check the Carburetors
As stated above, most running issues can be narrowed down to the carbs not working as designed. The carbs are a mechanical system that uses the venturi effect to draw gas out of the bowls and mix with the air before that mixture enters the engine. To see the venturi effect in action, take some compressed air and blow it right over the top of a straw that is in a glass of water.
There are a lot of small holes and channels in each carburetor that allow either gas or air pass through it. If any of those passageways are blocked, you will not get the proper fuel to air mixture for the engine to run. If you believe that this is your issue, I would recommend that you buy a carb rebuild kit. These usually include new seals to replace the ones you take off. Go through and use carb cleaner to clean the carbs completely and remove any blockages you find. The new seals ensure that they will not leak when you reassemble them. Using the old seals is usually not a good practice and may not seal correctly.
If you have already done this and you are still having problems, keep reading below to see some more reasons that will cause your motorcycle to not run correctly.
Check Fuel Quality and Connections
The fuel flow and quality of the fuel can greatly effect the running condition of the motorcycle. Dirty gas, tank, or fuel lines can gunk up the carbs and prevent the gas from getting into the engine.
But lets get the simple problem out of the way first. Make sure you have the petcock (the fuel valve) set to “On” or “Res” If it is set to off, gas will not flow from the tank to the engine.
If you fuel valve is in the correct position, good gas, and your carbs are cleaned and you are still having issues, there is more we can check. There are two more areas with the fuel that could be causing the gas not to flow correctly. The first is the fuel valve itself, or the fuel lines that connect everything together.
The Petcock (Fuel Valve)
The fuel valve (petcock) could not be letting fuel through because it is clogged up or the vacuum line is not opening it correctly. (If you have a vacuum style petcock) The way to tell which one you have is by seeing if there is a small vacuum line that connects the petcock to the engine intake. Another way to tell is if there are three tubes connected to it. Two are fuel lines (gas in and out) and the third one (which is usually smaller) is the vacuum line.
They way these work is rather simple. If there is no vacuum being pulled from the engine (the engine is off) the petcock will cut off fuel at the valve. When the engine is running and a vacuum is being pulled, it will open the petcock and allow fuel to pass through it. Even if the valve is set to “ON” the valve is actually closed if the engine is not running. They do this to prevent to much gas flowing into the carbs when the motorcycle is off. Early models of motorcycles required you to turn your fuel valve off overtime you got off the bike.
This was the problem I was having with my motorcycle. My vacuum line was cracked and not pulling the correct amount of vacuum to fully open my fuel valve. That tube is circled in the photo above. So during low demand (like riding at slow speeds) the bike would run fine, but when I went onto the highway it would run out of gas. After replacing that short line, my motorcycle has never had that problem again. The line only cost me a few dollars at my local auto parts store. I would just bring the old tube with you so they can match it up at the store.
Fuel Lines
The second problem that could be happening is the fuel line is collapsing and pinching off the fuel. This problem I have not run into myself, because I usually replace my fuel lines as soon as a get a older bike. But I did have a motorcycle technician tell me that some of the fuel lines could collapse after it heats up. Then when it cools down or you move it, it would open back up and the gas would flow again. It is a problem that hides itself very well.
If you think that this could be your issue change out your fuel lines, which should be pretty simple and will probably not need a lot of fuel line. I would cut a new piece of length to match the old one. In some rare cases you might need to find a OEM tube with the bends molded into it.
Check Air Filter and Airflow
If you believe it to be a air flow problem, the first thing you need to check is the air filter. They are usually located under your seat and can be replaced with relative ease. Having a dirty air filter will not allow enough air to flow through the carbs a pull gas into the engine. I had this issue with a old lawn mower.
The other things you need to look out for are nests that small animals leave behind. Old motorcycle have a lot of nooks and crannies that animals like to get into. My Nighthawk’s air box was filled with a bunch of seeds when I first bought it. Having something like a seed being sucked into your engine is really bad. The last thing we want is to have to replace the cylinder because of damage.
Other Less Common Things to Check
Some other things you could check include spark plugs, spark plug wires, choke cable, or vacuum leaks around the carbs. Any one of these items could also make the motorcycle stall out while running.
If the problem has started only after you replaced some part of the motorcycle, I would start there to make sure you (or someone else) installed the correct part in the correct way. For example; putting the wrong spark plus in could cause misfiring and stall out the bike under large throttle inputs.
The single best thing to do is to have a repair manual for your bike on hand when problems like this rear up. Older motorcycles will always have something going bad on them. Its just the nature of the beast, but I would not trade my motorcycle in for these reasons. Working on your motorcycle allows you to understand how it works and the more and more you work on your bike, the better you will get at figuring out what is wrong with it.
This is not something you have to learn overnight and if you are not comfortable doing something by yourself, get a friend to help you. It never hurts to have a extra set of eyes on a problem, especially if it is a really tricky problem. I know what it is like to ride a motorcycle that sometimes does not like to work and it can be stressful at times. But with each problem I fix, I feel a little more comfortable with the motorcycle and that feeling is absolutely fantastic.
If you are interested in what Motorcycle and gear I own, you can check it all out on the Bike and Gear page!