6 Simple Ways To Make Your Motorcycle Run Smooth: How to Fix It!

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If your motorcycle is running rich, you’ll usually be able to smell a difference in the exhaust if you pay attention. Don’t stick your face down by the exhaust , just stand next to the motorcycle while it’s running and if it smells really strong of fuel then that means your engine is running rich and you need to adjust your air to fuel ratio. There are several ways to do this.

Here are 6 ways to make your motorcycle run rich.

  • Adjust the ratio of air to fuel
  • Verify that the needle is not sticking to the carburetor.
  • Verify that there are no stuck open floats
  • Clean your air filter
  • Verify that the butterfly valves are not stuck open.
  • If your motorcycle is equipped with O2 sensors, replace them

The carburetor is most likely to be the culprit for a problem with running rich.  The carburetor is the most likely culprit for a running rich problem. When motorcycles are left sitting for long periods, fuel can gum up and cause strange problems to the carburetor.  The carb may become stuck together or clogged up and will require a thorough cleaning to get it back in working order.

Adjust the Fuel/Air Screw

A small screw is located on every carburetor. It’s called the fuel screw or idle screw. Manufacturers may call it something else.  However, its purpose is to adjust how much fuel gets sucked into the pistons before it combusts. You should first check if your bike is running low.

Older motorcycles can vibrate quite a lot while they run. This can lead to the fuel screw slipping out of the carb and allowing for more or less fuel.  Look in your manual under the carburetor section to determine if the screw should be twisted in or backed out.

On my 1969 Triumph, the service manual states that the screw should be turned all the way in the carb body until the bottom is out. Then turn it three revolutions back out. This will give you a good starting point to adjust the fuel to air ratio.  For more information on how to adjust the screw on your motorcycle, consult your service manual.

There are many other tools I love to keep close at hand that I use often on my motorcycles. Check out my list of recommended tools.

Sticking Needle

A carburetor’s main component is the needle.  It’s a long skinny metal shaft that lifts up and down when you twist the throttle.  If you remove the air filter from your motorcycle and look through its big hole, you will see the needle running through the middle.

The throttle lifts up when you use your hand to turn it. This allows fuel to flow.  If your carburetor hasn’t been cleaned in a while and you don’t ride it regularly enough then you might have issues with that needle sticking in the “up” Once you release the throttle, position. Because they become clogged up after being used, it can stick to the carburetor walls.

These are easy solutions.  It is best to remove the air filter from the engine so that you can see the huge hole in the carburetor.  You can turn the motorcycle off and move the needle with the throttle.

The cleaner will knock off a lot of gunk but if it’s really gummed up then you’ll probably have to take the carburetor all the way off the motorcycle and take it apart to clean it thoroughly.

Open Floats Stuck

It is also easy to fix stuck open floats and it will only take an hour to do so. You may notice a few signs such as running rich or fuel overflowing from the carburetor. I’ve seen all three first hand on different motorcycles I’ve owned.

Floats are tiny bubbles that sit in a carburetor bowl.  If you remove the bowl (usually 3 to 4 screws at the bottom of your carburetor), the floats will fall down a bit.  It’s similar to looking inside any toilet tank. A float is the big bubble that rises and falls with the water level. One is in each bowl of your carburetor.

Before you start taking apart anything, be sure to take pictures with your smartphone. You think you’re going to remember how to put everything back together but I promise you won’t.  I’m speaking from years of experience rebuilding carburetors.

In order to clean the floats and make sure they aren’t sticking, just take off the bowl and there will be one pin in each float.  Use a small pointed object to push the pin out of the side. The float will fall free.

A small piece is attached to each float and looks like a tiny missile.  The stopper is what you call it. This shuts off the fuel flow from your tank once the level in your carburetor has reached a high enough. It’s a cool little feature so your engine doesn’t flood constantly.

This is definitely a lot easier to do if the carburetor is completely off of the motorcycle but it doesn’t have to be. After taking out the stopper and float, clean the carburetor with carburetor cleaner. Even a small toothpick can be used to clean the interior walls of the stopper. This will help the stopper sit more comfortably.

Every section of the carburetor comes with its own stopper and float. If you don’t know which cylinder is the problem, make sure to clean them all thoroughly.  You should clean the stopper, pin, and float thoroughly before you put them back. You should find it easy to push the pin in or out. If it’s tight then you did something wrong and you need to take it back out again.

You should ensure that the float flips up and down easily. It should be able rotate up and downward by simply jiggling its carburetor.

I have made a video series on how to restore motorcycles. This series also includes a detailed 25-minute video on how to clean carburetors and rebuild them. You will also find other components that are difficult to tackle, such as the body and electrical. 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!

Clean Your Air Filter

This is one that so many people overlook because they don’t think about an air filter causing a fuel problem.  In order for your motorcycle to run properly it needs 14.7 parts of air to every 1 part of fuel, that’s called the air to fuel ratio.  If you have a clogged air filter then that ratio will get reduced down to 10:1 or 8:1 and you’ll be running rich.

When an air filter is old, is has a lot of trapped dirt and debris inside the small foam pockets and it doesn’t let the air flow as smoothly through it. This can cause air restriction and make your engine run less efficiently. They’re usually only a few dollars online, so go ahead and change yours if it has been a few years since you’ve done it.

Every motorcycle is a little different in how you change your air filter, but the manufacturers make it really easy most of the time because it’s something you should change at least every few years.  Some motorcycles have two filters: one for the pre and one for the post. Check your user’s manual to figure out how to change your specific filter. You can find this article that I wrote about air boxes and pod filters.

Open the Butterfly Valve

The butterfly valve, which is located on each carburetor port, is the circular disc that opens and closes depending on how you twist it with your hand. These valves are controlled by really tightly wound springs on the carb body and if one of those springs breaks or gets loose then the valve won’t shut properly.

One time, I was helping a friend work on his motorcycle. His problem was that every time he tried to twist the throttle, the motorcycle would stall.  I discovered that someone had changed the springs. The throttle would shut off the butterfly valve every time he turned the throttle, making the motorcycle stop.

Running rich can also happen.  The valve can get stuck and too much fuel will continue to flow into the cylinder. Instead of the throttle being controlled by the rotation of your hands, it will cause a running rich issue.

In order to see if this is a problem with your motorcycle, you’ll have to take the air filter off and look through the carb hole as you twist the throttle cable.  If you open the throttle and the flapper opens at the same rate then it’s working properly. If not, then you know that’s what the issue is.

If you have an O2 sensor, change it

Modern motorcycles are often fuel injected.  You have a fuel-injected motorcycle, which means that you will not have to worry about the above points.

O2 sensors are responsible for most of the motorcycle’s running-rich issues. Over their lifetime, O2 sensors experience heat cycles that can be quite intense. They can get extremely hot while the engine is running. Then they become very cold when it stops. This causes them over time to fail.  If you are experiencing constant problems with running rich, I suggest that you replace your O2 sensors.

Not all fuel injected motorcycles have O2 sensors, but for those that do, it’s a common problem for that sensor to send misinformation to the ECU and tell the fuel injectors to spray more fuel into the cylinder on each rotation.

Similar Questions

How often should my carburetor be rebuilt? A carburetor may not be necessary if your motorcycle is used regularly.  If you don’t use your carburetors, they can get clogged up. So go out and ride as often as possible!

What are the best tools you can use to clean a carburetor A simple socket set is my favorite tool for cleaning carburetors. I also use a pick with a 90-degree bend at the end and small screwdrivers.  Drill bits are great for cleaning out jet ports.

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