50cc Dirt Bike Won't Start: Work Through This List in Order

Before you assume the engine is bad, know this: on a 50cc two stroke, a no start is almost never the engine. It is fuel getting to the carburetor, a choke in the wrong position, or a kill switch nobody noticed. Work down this list in order and do not skip ahead.

Start here, the free stuff

1. Kill switch and tether. If your bike has one and it is pulled or off, the bike will not produce spark at all. It will crank forever and never fire. Check this first, every time.
2. Fuel valve. The small tap under the tank. OFF means the carb runs on whatever is in the bowl and then dies. Turn it to ON.
3. Fuel actually in the tank. Look in it. Do not go by the weight of the bike.
4. Choke position. Cold engine wants the choke down. Warm engine wants it up. Getting this backwards is the second most common cause.

If it now starts, you are done. Most calls end here.

If the cord itself is the problem, it will not pull back, it feels loose, or it pulls out and stays out, that is a separate job. We wrote it up here: how to fix a 50cc dirt bike pull start.

It cranks and fires, then dies after a few seconds

Classic fuel starvation. The engine burns what is in the carburetor bowl and gets no more. If this is exactly your symptom, the long version is here: dirt bike starts then dies, what the carburetor is telling you.

• Fuel valve again. Genuinely, check it again.
• Choke left on. If you never pushed it back up after it fired, it is drowning in fuel.
• Old fuel. Mixed gas breaks down in about 30 days. Old fuel gives you exactly this symptom. Drain it and mix fresh.
• Wrong mix. Too much oil bogs and fouls. If the ratio has been guessed at a few times, the carb may be gummed, and the bike will usually smoke more than it should as well. Correct ratio is 25 to 1, which is 5.12 oz of two stroke oil per gallon.
• Blocked fuel cap vent. A sealed cap creates a vacuum in the tank and stops fuel flowing. Crack the cap loose and try again. If it runs with the cap loose, the vent is your problem.

It cranks but never fires at all

Now check spark and flooding.

• Pull the spark plug. This tells you nearly everything.
  • Soaking wet means flooded. Leave the plug out, choke off, throttle wide open, pull the cord six to eight times to clear the cylinder. Dry the plug, refit, start again from the top.
  • Black and crusty means fouled from too much oil or too much choke. Clean it with a wire brush or replace it. Plugs are a few dollars. The plug tells you more than that, and here is how to read a two stroke spark plug properly.
  • Bone dry means no fuel is arriving. Go back to the fuel section.
• Loose plug cap. Push the boot firmly onto the plug. They vibrate loose.
• Flooded from over pulling. If you have pulled twenty times in frustration, it is flooded now regardless of what it was before. Clear it as above.

It runs but will not idle, or bogs when you open the throttle

• Choke still partly on. Most common.
• Idle screw. There is an idle adjustment on the carburetor. A quarter turn at a time, not half a turn.
• Governor screwed all the way in. If the speed limiter is wound right down the bike will barely rev. That is it working as intended, not a fault.
• Air filter. If it is caked in dust the engine cannot breathe. Pull it, look at it, and clean it properly if it is dirty.

What not to do

• Do not keep pulling. After about ten pulls with no fire you are flooding it and making the job harder.
• Do not add starting fluid. On a two stroke it washes the oil off the cylinder wall. People have seized engines doing this.
• Do not run it on straight gas to "test" it. Not for one minute. A two stroke gets all its lubrication from the oil in the fuel.
• Do not take the carb apart on day one. Ninety percent of no starts are solved above without touching a tool.

Still nothing

Send us a short video at pluggedbycc@gmail.com showing the fuel valve, the choke position, and you pulling the cord. Include the name the order was placed under and your purchase date. We spot it in the video most of the time, and if a part came through defective we take the claim to the factory on your behalf and get the correct part sent out free.

Related: the correct cold start order, how to mix fuel at 25 to 1, how to read a spark plug and how to clean the air filter. Full walkthroughs with video at manual.pluggedby50cc.com.

Off road use only. Helmet and gear every ride, and an adult supervising.

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.