Carburetors installed on your engine uses needle valves in the float to either stop the flow of fuel or add fuel to the float bowl. The needle valve flow control allows the carburetor to maintain the required amount of gas on the float bowl.

Needle valves, sometimes referred to as plunger valves, are regulating valves and enable engineers to finely control and regulate water flow and pressure.

The difference is precision. Needle valves are similar in design to globe valves. The primary difference is the valve seat and the needle shape. Needle valves are valued for their use in calibration because they can be so finely tuned.

When fuel is drawn up the main jet, the fuel level in the chamber drops, thus the float also drops. This opens the needle valve allowing more fuel to enter the chamber. When the float again rises with the fuel level, the needle valve will close off the fuel supply.

Symptoms of a Bad or Failing Carburetor

• Reduced engine performance. One of the first symptoms commonly associated with a bad or failing carburetor is a reduced engine performance.
• Black smoke from exhaust. Another symptom commonly associated with a problematic carburetor is black smoke coming from the exhaust.
• Backfiring or overheating.
• Hard starting.

Use carburetor cleaner to remove deposits, clogs & debris Deposits inside the carburetor can clog fuel and air passages and reduce performance or stop the engine altogether. Luckily, you can take care of many of these problems quickly and easily; often without even removing the carburetor from the engine.

Rebuilding a Carburetor is Better than Replacing It The internal parts and gaskets can deteriorate and cause multiple problems. There’s also some moving parts inside like the float and the needle and seat. In addition, the gas that sits in the fuel bowl can deteriorate and start to varnish parts inside the carburetor.

Watch for certain signs and symptoms if you suspect the carburetor float is sticking.

1. Engine Won’t Idle. One of the signs that the carburetor float is sticking is when the engine will not idle.
2. Flooded Carburetor.
3. Engine Stalls or Hesitates.
4. Engine Misfiring.

Tap the top of the carburetor gently but firmly with a small hammer or screwdriver handle. Tap the bowl of the carburetor firmly. This may loosen a stuck float valve, allowing the float to work properly until you can fix the problem permanently.

Soak it in fuel or alcohol and work it open and shut. It will free up. Put the carb in hot (not boiling) water for a while then try to move the barrel while it’s still hot. Don’t forget to use gloves!

One of the more common questions we get concerns either the overwhelming smell of gas coming from the carburetor or fuel leaking out of the bowl or overflow. Both conditions are typically caused by a stuck or worn float needle valve. Another common cause is the use of fuel containing any Ethanol.

Registered. A float that is sticking is most likely caused by either varnish on it which gums up the valve or a misshaped needle valve that does not seal good all the time or dirt in the carb bowl.

The float height adjustment will mostly affect only part throttle openings.It has a static setting that,when at idle,the float valve will open only very small amounts.At WOT (Wide-Open-Throttle) the float will be at its lowest for full fuel flow,so the height adjustment will not affect WOT.

Running lean can give you more power but to lean will blow your engine. Running too rich can also hurt your motor. Think of it when you are mixing gas for your weed wacker. It is always safe to add a little more oil than not enough to the mixture.

Signs Of Your Engine Running Lean

1. 1: Bad Performance. Your car will have less power than it had before.
2. 2: Car Won’t Start. Your may have trouble starting your car, or your engine may not turn over.
3. 3: Spark Plugs Are Clean Or White. A common symptom of your car running lean is that your spark plugs are clean or turn white.

A low float height makes the bike run rich and a high height makes it run lean. If the float does not measure to spec, adjust it by bending the tang up to allow a higher float or down to lower the height. Tang: Metal adjustable tab that determines the height of the floats.

The float level determines how soon the main jet feeds gas. Think how much easier it is to siphon gas from a full gas can than one that’s half or a quarter full. That’s kind of how a carb works, it’s got to draw the gas from the bowl up to the discharge nozzle and down into the intake.

Turn the screw clockwise until the engine starts to sound rough.

1. Tightening the screw weakens the air and fuel mixture and decreases the amount of fuel flowing to the engine.
2. Tightening the screw is also called making the fuel mixture leaner, which lowers the RPMs at which the engine idles.

Locate the idle mixture screw and turn it clockwise until the needle lightly touches the seat. Then, turn the screw counterclockwise 1-1/2 turns. If your carburettor has a main jet adjustment screw at the base of the float bowl, turn the screw clockwise until you feel it just touch the seat inside the emulsion tube.

Float level is too high If the float height is too high, this will cause the fuel to rise to a level above the operational spec. If the fuel height is a bit too high and the bike is running, the engine will display a rich running condition, which will make the throttle response slow and the engine note muffled.

The throttle valve will have a “cutaway” on the air box/intake side of the carburetor, and it basically impacts the pressure signal across the pilot and needle jet. So by altering the cutaway size on the throttle valve, the pressure/signal of airflow through the carburetor can be changed.

Start turning air screw counter clock wise, ¼ turn at a time until you have reached 2 ¾ turns out. Between 1 ¼ and 2 ¼ turns, your engine should have reached its highest RPM maintaining a steady throttle. Adjust air screw again between 1 ¼ and 2 ¼ until you have determined highest RPM.

For example, using too large of a main jet will cause more fuel to enter the combustion chamber than it can efficiently burn. This will result in a “sputter” at full throttle. It could best be described as a rapid misfire.

The first thing to do is not set up the idle speed, but to set the Idle mixture screw to lean best idle setting. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). The engine should pick up speed and begin to smooth out.

Carb Quick Guide

1. Verify carburetor is set to stock settings:
2. Start bike, bring to operating temperature.
3. Set idle speed adjusting screw, clockwise to increase rpm, counter-clockwise to decrease rpm.
4. Adjust idle mixture by turning idle mixture screw slowly clockwise until the engine runs poorly.