A lot of your engine problems such as the engine not idling or the engine dying out can be easily solved with minor adjustments in the carburetor.
In this article, you can learn how to adjust the idle screw and the air/fuel mixture screw for both the stock carb that comes with the predator 212 (or other small engine honda clones) and the Mikuni carb and its clones.
Stock Carburetor Adjustments
The stock carb that comes in with the Predator 212 or other clone engines will look similar to this:
The idle screw is located just above the idle jet (Use the above image for reference)
The function of the idle screw: The idle screw will determine how much the throttle closes in idle conditions. If you turn in the idle screw it will prevent complete closing of the throttle when the engine is idling and therefore increase the idle speed.
Similarly, if you loosen the screw, the throttle will close completely in idle condition and decrease the idle speed.
Adjusting the idle screw: If you want the engine to have higher rpm while idling, you’ll need to tighten the screw so that the throttle doesn’t close completely on idle and vice-versa if you want lower rpm then loosen the screw.
Air-Fuel mixture screw
Refer to the image above for the location.
Function: The air-fuel mixture screw is going to control the amount of air that enters the engine. If you tighten the screw it will make the mixture rich and if you loosen the screw, the mixture will be lean.
Adjusting the Air-Fuel Ratio: Before we discuss any adjustments, the important thing to note is that most of the new Predator 212’s stock carbs are non-adjustable, this is due to government regulations to protect the environment.
If your air-fuel mixture screw is fixed, then you’ll need to either clean your carburetor or change your idle and main jet to fix your carburetor issues. Unfortunately, you can’t just make a quick adjustment.
But if you do have an adjustable screw, then you can tighten the screw for a richer mix and loosen the screw for a leaner mixture.
Step by Step process:
- Keep your engine running.
- First adjust the idle screw to an idle speed of your liking.
- Observe the sound the engine is making. If your mixture is too rich, the engine will sputter and if the mix is too lean the engine will produce bogging sound.
- Tighten the air-fuel screw if the engine is bogging and loosen the screw when the engine is sputtering. Find the balance.
Mikuni Carburetor Adjustment
Mikuni VM22 and its clones are the popular carb upgrade for go-karts and mini bikes, they are not as simple a design as the stock carburetors.
Note: Most of the Chikuni/Mikuni carbs come with a #98 main jet which isn’t big enough if you have a stage 1 air filter installed, the engine will run lean. In such cases, you need to first get a bigger jet (at least #120), adjustment alone won’t fix your issue.
Use this image as a reference for screws in the VM22 Mikuni.
Step by Step:
- Take your screwdriven and turn the Air/fuel screw all the way in but not too tight.
- Now loosen the air/fuel screw to 1 and 1/2 turns out
- Start your engine
- Once the engine starts running, tighten or loosen the screw 1/4 turn at a time and take note of the rpm. You need to find the position at which the idle rpm is maximum.
- Keep making 1/4 turns untill you find the maximum rpm.
- Once you find the highest idle rpm position, loosen the idle screw.
If the throttle responsiveness isn’t good then it’s usually due to lean mixture, you’ll need to adjust the needle in such a situation, check this article to understand how the Mikuni works and how to adjust the needle valves.
What to do if your Carburetor doesn’t have an Adjustable air-Fuel Screw
Most of your carburetor issues can be solved by cleaning the main jet and the pilot jet. If the engine isn’t starting or it’s starting but dies out at half or full throttle, you will need to take your carb apart and clean all the components.
Sometimes, bad fuel can also cause these issues so make sure to check your fuel tank.
Basically, having an adjustable screw allows for a quick fix, so not having one will require more work.