It can be incredibly frustrating when it comes to mechanical issues on a motorcycle. Just like any other vehicle, one problem could be caused by several different factors and sometimes it’s hard to know where to start looking.
A high idle on a motorcycle is no exception. Not only is it annoying, but a high idle can be dangerous for you and your motorcycle. Figuring out the problem as soon as possible is always a good idea.
So, why is my motorcycle idling high? A motorcycle idles high when it is getting too much of an air and fuel mixture in a low speed or neutral position. This is usually caused by the idle screw on the carburetor being out of adjustment, an out of place throttle handle screw, a bad carburetor throttle spring, or a sticky throttle or throttle cable.
Fixing motorcycle issues such as a high idle doesn’t always have to be a scary experience. I have been fixing and restoring motorcycles myself for the past six years and can provide a helpful guide to aide in your navigation towards fixing your motorcycle.
Why A Motorcycle Idles High
I can’t tell you how many times I’ve gone to start up a motorcycle only to be startled by the loud noise of a high rev that it starts with and continues to idle high. I have mostly owned older motorcycles, so the sound of the high idle isn’t exactly super pleasant.
You’re not alone if you’ve found yourself in this situation. Many motorcycles, especially older motorcycles with a carburetor, often have this problem. It’s a good idea to be come familiar with the signs and symptoms of a high idle and know how to tackle the problem because chances are you’ll likely run in to it again.
A motorcycle idles high because there is more fuel and air mixture being sucked into the engine and combusting. The greater combustion causes the pistons to stroke faster and the crankshaft to spin faster. This also causes greater exhaust flow out of the exhaust pipe and pushes more air out which is why it is louder.
The first and most common reason a motorcycle idles high is due to the air and idle screw turned too high. This is a screw that is designed to keep the throttle plate from closing completely. It is found on your carburetor that you are able to turn and adjust and is a tool that will raise and lower the throttle.
Each carburetor on a motorcycle is different so the idle screw is found in different places and also may look different compared to others. Refer to your owner’s manual to locate where it is and attempt to adjust it with a screw driver and see how your motorcycle reacts.
Sometimes there is a stop switch or a set screw somewhere on the right hand throttle. This is designed to keep the throttle in place. Occasionally that screw will become out of place and won’t let your throttle release all the way so your motorcycle will constantly be throttled a little bit.
You can usually tell if this is the cause of the problem because the throttle isn’t doing a full turn. Examine your throttle and see if there is a set screw holding your throttle in place. If there is one, adjust it to ensure your throttle has all the space it needs to twist back and forth without any obstruction.
If you have a carburetor, there is a spring that is pulled on it when the throttle is twisted. This is used to spring back the throttle into the idle position when it is let go or released.
If that spring on the carburetor gets old or malfunctions, it won’t pull back the throttle to the idle position and also won’t close the butterfly valve inside the carburetor which leaves you in a high throttle position.
To see if this is your problem, trace the throttle cable back to the carburetor and examine the spring it is connected to. If you notice it’s stretched too much or simply missing, replace it.
Sometimes the throttle can also be stuck to a high idle position because of gunk and grime that gets either underneath it. Grime and sticky substances can also get inside the throttle cable and cause that to malfunction as well.
I had a CB650 that actually had both of these issues. I took apart the throttle on the right hand side and it was full of gunk and a strange stickiness. I cleaned that as well as squirted some oil down the throttle cable lining and there was a bunch of gunk that washed out.
If you have a fuel injected motorcycle, please note that most of these types of motorcycles briefly idle high right after it is started and then lowers. This is so the motorcycle can get up to operating temperature quickly. This is completely normal and is nothing to worry too much about.
I have created a video series about restoring motorcycles from start to finish and within this series includes a detailed 25 minute video on how to clean and rebuild carburetors. This series also includes other hard-to-tackle components such as body work 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!
The Risks Of Riding With A High Idle
If you notice your motorcycle is idling high, it’s important to quickly address the issues and keep that from happening because there are a few risks involved if you continue riding like that.
Having a high idle means the motorcycle is getting power but isn’t using it because it’s stopping itself due to either the brakes, it’s in neutral, or it’s in a low gear. The power that is building up with a high idle while riding can manifest itself at unexpected times.
For example, if you come to a stop on the road either in traffic or at a stop sign, letting off the break a little bit can take you a lot further than you want to go because there’s so much power building up. You may end up rear-ending someone or accidentally running a stop sign.
There are also risks involved with your motorcycle if you’re riding with a high idle. Your motorcycle may shift really hard in between gears and you may even hear a loud clunking noise. This can later cause issues with your transmission and clutch because a hard shift like that isn’t good for the gears.
What RPM’s Your Motorcycle Should Be At
Having your motorcycle maintaining the right RPM’s is vital for it’s health. A motorcycle shouldn’t be at constant high RPM’s because that will wear out the engine a lot faster as well as rattle your ears and everyone else’s around you.
In combustion engines, the idle speed is usually measured in revolutions per minute of the crankshaft, or RPM’s. A good idle speed will generate the right amount of power to get the motorcycle going then increase to whatever you’d like it to be as you get going down the road.
A healthy RPM for most motorcycles should be between 700 RPM’s – 1,000 RPM’s. Some motorcycles are a little different from each other, so be sure to check your owner’s manual to make sure. But usually you can tell by how it sounds. Any idle higher than 1,500 RPM’s is considered high and should be adjusted.
How To Prevent High Idle
A high idle on a motorcycle is one of those issues that can either slowly start to increase in intensity or it can completely surprise you with how high it is once your start up your motorcycle.
Some of the possible causes of a high idle are hard to prevent unless you are willing to look at every nut and bolt of your motorcycle routinely. The causes of a high idle are usually pretty easy to fix, so it’s usually no big deal when you find yourself having this issue.
One good practice to always pursue is maintaining the health of your throttle and throttle cable. Make sure these two items are always away from anything that could potentially spill on them and cause them to stick. Avoid parking under sappy trees or leaving your motorcycle out in the elements without a cover.
Why does a motorcycle lose power when accelerating? There are several reasons why a motorcycle loses power when accelerating. Some reasons include a broken carburetor spring, a vacuum leak, extra slack in the throttle cable, and poor timing advance. Click here to see my full list of why a motorcycle loses power when accelerating.
Does a motorcycle battery charge while idling? A motorcycle does charge it’s battery while it is running. The battery is what is used to start up the motorcycle and the stator is what keeps the motorcycle running while also charging the battery so the battery can continue to start the motorcycle in the future.