Go-karts might be small machines, but they can be complex at times too. Troubleshooting issues with engine behavior can be difficult as there may be several causes for the same problem, and one such problem is the go-kart taking off when you start it.
The most common cause for go-karts taking off after being started is a faulty or worn clutch. It can also be caused by a faulty or stuck throttle cable, or the engine idle settings. Luckily, all of these are quick and easy fixes to ensure that your kart idles properly when the engine is started.
Your go-kart should be able to idle without moving forwards or without shutting down by itself. Having a kart that wants to move forward when the engine is idling is a common problem that many drivers experience. We take a closer look at the reasons for this below.
Why Your Go-Kart Is Taking Off When You Start It
The main reasons your go-kart might be taking off when you start it are:
- You have a worn out clutch
- Your engine is revving too high
- You have a faulty throttle cable
- Your jetting settings are off
Karts should be able to idle on their own without having to press the throttle or hold down the brakes. Just like a car, this idling process should be smooth and easy, and if you find that your kart is taking off when you start it, then something is wrong.
The kart will still work perfectly fine, but it could be a sign that you need to do some maintenance or adjust some settings on the engine. Let’s look at some potential reasons why your kart might be moving forward while idling.
Worn Out Clutch
The first potential reason why your kart is taking off when you start the engine is that the clutch needs maintenance. The clutch is an integral part of the kart because it’s responsible for converting the engine’s power into forward motion. When the clutch is faulty, the kart will behave strangely.
Karts don’t have the same clutches as cars. Karts use a centrifugal clutch, which means that the shoes (small metal blocks) inside the clutch housing need to spin and be forced outwards into the edges of the housing.
The faster the clutch spins, the stronger the force pushing the shoes into the edges of the housing. However, these shoes can often break into pieces because of the severe forces being put through them. In this case, you could have a kart that struggles to idle and behaves strangely when idling.
The clutch bushing and housing also needs to be properly lubricated. If the bushing is not lubricated, the kart’s engine will struggle to idle because more force needs to be put into the clutch to keep the shoes spinning at the correct rate inside the housing.
Engine Idle Settings Too High
The tiny two-stroke engines in racing go-karts need the perfect conditions before they perform at their peak level. This idea of ideal operating conditions also applies when it comes to the kart’s engine idling speed.
Rotax karts have a specific setting that allows the driver to adjust the engine idling RPM. However, this setting is not perfect for all conditions, and it may need to be adjusted based on variables such as temperature and humidity.
If the engine’s idling speed is too high, the kart will move forward when the engine is started. This means that the kart cannot idle at a standstill and the driver will need to keep their foot on the brakes while the engine is idling. If the idling speed is too low, the engine will simply cut out when the kart is standing still.
Faulty Throttle Cable
Go-karts use a simple cable to control the throttle. The cable is attached to the pedal on the right hand side and it runs all the way along the chassis and into the engine. This cable is solely responsible for driving up the RPMs in the engine and controlling the amount of power the engine is producing.
You can even pull this cable to rev the engine without touching the throttle pedal. These cables are not immune to faults, or even to getting hooked on something. If your kart is lurching forward and accelerating as soon as you start the engine, it could be something as simple as a faulty throttle cable.
If your kart has been serviced recently, it could be that the cable was tightened too much and is causing the engine to rev even if the throttle pedal is not being pushed down. It could also be that the throttle cable has gotten hooked on a part of the chassis and is causing the engine RPM to rise.
Incorrect Jetting Settings
Like the idling settings, the jetting and needle settings inside the carburetor are also important. We know that the jetting of the Rotax engine needs to be spot on or else you’ll have backfiring, flooded carburetors, and all other kinds of performance gremlins.
However, having the incorrect jetting or needle settings can also impact the idling of your kart’s engine. The jetting of your carburetor affects how much fuel flows into the engine, so if the engine is sending too much fuel into the combustion chamber, it could cause the engine to rev higher once you start it.
This could cause your kart to take off when the engine starts. The opposite could also happen in some cases where the engine would simply cut out because it’s not getting enough fuel. It’s all about the weather conditions and how they impact the amount of fuel and air that needs to be mixed inside the engine.
How To Stop Your Kart Taking Off When You Start It
Maintain Your Clutch
First of all, the clutch is crucial. It’s the most common cause for the kart to take off when you start it. You need to make sure that you’re constantly maintaining your clutch. At the very least you should be opening it and inspecting the clutch shoes once a month to ensure that they are still intact and working properly.
You can do a full service of your clutch once a month too, but that takes some additional time and effort. In the long run it’s worth doing a complete clutch service once a month to ensure that it’s always running smoothly. You simply need to remove the entire clutch and clean the inside of the housing with brake cleaner.
You also need to use grease to lubricate the clutch bushing when removing and reinstalling the clutch. This will ensure that it runs smoothly. You can inspect each clutch shoe individually to ensure that they are not damaged or cracking in any way. If they’re showing signs of wear, it’s best to replace them.
Adjust Your Engine Idle Settings
High engine idle speed is also a common cause for the kart taking off when the engine is started. If the engine idling speed is too high, the RPM will cause the kart to move forward and require the driver to keep their foot on the brakes even while the engine is idling. This will also put strain on the clutch and wear it out faster.
Adjusting the engine idle speed is incredibly easy. All you need to do is turn the screw next to the carburetor. This is often referred to as the engine idling screw. Its only purpose is to adjust the RPMs that the engine will idle at, which shows that it’s such a common issue that many engine manufacturers have even made it easy to adjust!
Turning the engine idling screw clockwise will increase the idling RPM, and turning the screw anticlockwise will decrease the engine RPM. If you have a MyChron device you can easily measure the RPMs. The ideal idling RPM for Rotax karts is usually between 950 and 1800 RPM depending on the weather conditions.
Check Your Throttle Cable
Another quick fix is to check the throttle cable. This cable will run from the engine all the way to the throttle pedal. You can simply pull the cable away from the pedal (towards the engine) to see if the engine RPMs decrease.
If there is no pressure on the throttle pedal, the engine should be idling. So, if you notice the RPMs decreasing when you pull on the throttle cable, it means that it was set too tight. You will need to loosen it and adjust the slack on the cable to be more accurate.
If you make the throttle cable too loose, you will struggle with throttle response. The ideal throttle cable tightness is when the slightest bit of pressure applied to the throttle pedal causes the RPMs to increase immediately. Loose cables will cause a delay in acceleration.
You can also follow the cable along the chassis to see if it’s catching on any parts of the kart and causing a sudden surge of engine power when the kart is started. This can sometimes happen if the kart has been through a tough race and has picked up some dirt or damage along the way.
Change Your Jetting Settings
The jetting of your kart’s engine is always important. It’s something that needs to be adjusted every time you bring your kart out of storage, and sometimes it even needs to be adjusted throughout the course of the race day.
Having the incorrect jetting and needle settings for your engine can cause it to take off when the engine is started. That’s why you need to make sure to check your local weather and use the corresponding jets and needle settings at all times.
It’s incredibly quick and easy to change the jets and the needle position in the carburetor, so there should always be time to get it done.
Your kart is supposed to idle without moving forward or cutting the engine. If your kart is taking off when you start it, then it’s an indication that it needs some maintenance. The most common cause is a faulty or worn out clutch. Having too high an engine idling speed, a faulty throttle cable, and the wrong jetting settings can also cause this problem.
I created and have been writing on this site since 2019, collaborating with drivers, coaches, engineers and manufacturers to provide you with the most reliable information about motorsport. Find out more about me here.