The short answer
The speed limiter on a 50cc dirt bike is a small screw with a lock nut, threaded into the top of the carburetor where the throttle cable enters. Turning it in (clockwise) makes the bike slower. Turning it out (counterclockwise) makes it faster. Screw it all the way in for a first-time rider, then back it out a quarter turn at a time as they earn it.
That's the whole job. Here's how to do it properly and what to watch for. If you are still choosing a bike, our guide to what size dirt bike suits a 6, 8 or 10 year old covers fit, how to choose the right 50cc dirt bike for your child covers the buying decision itself, and the safety tips for beginner riders cover the gear that goes with a slower setting.
What the limiter actually does
It is not an electronic speed setting. It is a physical stop. The screw sits in the path of the throttle slide inside the carburetor, and it stops the slide from lifting all the way. With the screw in far enough, the slide can only open a fraction of the way, so the engine can only make a fraction of its power.
That means the rider can pin the throttle to the stop and the bike still cannot exceed the speed you set. A kid cannot override it by twisting harder, and they cannot accidentally find full power by panicking. This is the single most useful safety feature on a kid's dirt bike.
Where to find it
Look at the carburetor, on the right side of the engine. The throttle cable comes down from the handlebar and enters the top of the carb through a threaded cap. Right there, either on that cap or immediately beside it, is a small screw with a lock nut on it.
On some bikes there are two screws in that area. The one you want is the one the throttle cable runs through or sits directly next to. The other one, usually further down the carb body and often with a spring under it, is the idle screw. Leave the idle screw alone for now, it does a different job.
If you are not sure which is which, back one out slightly with the engine off, then open the throttle by hand and watch. The limiter screw changes how far the throttle will physically travel. The idle screw does not.
How to adjust it, step by step
- Engine off and cold. No reason to do this with a hot exhaust an inch from your hand.
- Loosen the lock nut on the limiter screw with a small wrench. Usually 8 or 10 mm. Just enough that the screw turns freely.
- Turn the screw all the way in, clockwise, until it lightly seats. Do not force it. This is your slowest setting.
- Back it out one full turn. That is a sensible starting point for a brand new rider.
- Snug the lock nut back down against the cap while holding the screw still with a screwdriver, so it can't vibrate its way looser while they ride.
- Test it yourself first. Start the bike, hold the front brake, and roll the throttle to the stop to hear where it tops out. Then ride it slowly down the driveway before you hand it over.
How to open it up over time
Resist the urge to jump straight to wide open because they asked nicely. Speed is the last thing a new rider should get. If you have not run a first lesson yet, read how to teach a kid to ride a dirt bike first, then come back and set the screw to match.
- Session 1 to 5. Screw nearly all the way in. Walking to jogging pace, roughly 5 to 10 mph. Flat, open ground with nothing to hit. This is where they learn the throttle feel, the brakes, and how the bike behaves when they let off.
- Once they can stop on command, every time. Back it out another half turn. If they cannot reliably stop where you point, they do not get more speed. That is the rule.
- Once they can ride a circle both directions without putting a foot down. Another half turn.
- Once they are looking ahead instead of at the front fender. This is the real tell that a rider is ready for more. Keep opening it up in small steps from here.
- Wide open. About 32 mph, and our full breakdown of how fast a 50cc dirt bike goes covers what changes it. Most kids are somewhere around 10 to 12 before this makes sense, but go by the riding, not the birthday. If you are working out whether your kid is ready at all, what age should a child start riding a dirt bike goes through it.
Common problems
The bike idles too high after I adjusted it
You turned the idle screw, not the limiter. Back it out until the engine idles steadily without the rear wheel trying to creep forward, then find the correct screw and start over.
It won't go any slower even screwed all the way in
Check the throttle cable free play at the handlebar. If the cable is adjusted too tight, it is already holding the slide partially open before anyone touches the twist grip. There is a small barrel adjuster where the cable meets the throttle housing. Back it off until you have a few millimetres of slack in the grip before the throttle starts to move.
The setting keeps changing on its own
The lock nut is not tight. Two-strokes vibrate hard and a screw that is not locked down will walk out. Hold the screw with a screwdriver while you snug the nut.
The bike bogs and won't pull at all
You may have gone too far in, or you may be chasing a fuel problem rather than a limiter problem. If it bogs even with the limiter opened up, start with the wont start checklist and check your fuel mix at 25 to 1. A bike that bogs and smokes heavily is usually running too much oil, and a clogged air filter does the same thing.
When a rider has honestly outgrown the 50cc at wide open, the step up is electric. The Sykeruns X5 and the Sykeruns X7 are sized for teens and adults.
One thing parents get wrong
The limiter is not a substitute for supervision, gear, or picking safe ground to ride on. A bike doing 8 mph can still put a kid down hard on gravel. Helmet, gloves, boots, long sleeves, eye protection, every single ride, at every setting. Our kids dirt bike safety gear guide lists what actually matters and what you can skip.
Questions on your specific bike? Text 623 320 8984 and we'll talk you through it. Full setup walkthroughs live at manual.pluggedby50cc.com.
Plugged by 50CC is an independent retailer. We do not manufacture, assemble, modify or service the bikes we sell. Every bike ships sealed in its factory crate exactly as it reaches us, about 90% assembled from the factory, and final assembly and setup are completed by the buyer. Off-road use only. Riders under 18 should always be supervised by an adult.