For the combustion process to take place in a gasoline engine, the minimum AFR is around 6:1 and the maximum can go up to 20:1. When the air-fuel ratio is higher than the stoichiometric ratio, the air-fuel mixture is called lean….Air-fuel ratio, lambda and engine performance.

Lambda represents the ratio of the amount of oxygen actually present in a combustion chamber compared to the amount that should have been present in order to obtain “perfect” combustion. If a mixture contains too little oxygen for the amount of fuel (a rich mixture), lambda will be less than 1.00.

Oxygen/Combustibles balance ( Lambda ), is calculated from the measured values of O2, CO, CO2, HC, NOx and Water Vapour in the exhaust gas. Once Lambda is calculated, A/F Ratio can be easily determined by simply multiplying Lambda times the Stoichiometric A/F ratio for the fuel used – e.g. 14.71 for petrol – gasoline.

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.

Running lean, on the other hand, refers to when a car’s engine receives too much air and too little fuel. When this occurs, you may notice symptoms like sluggish acceleration as well as jerking. Some of the most common causes of a lean-running engine include clogged fuel injections, bad fuel pump and a vacuum leak.

A yellowish or blistered appearance on the spark plug electrode would tell you the A/F mixture is much too lean (or the spark plugs are too hot and the engine needs colder plugs). Heavy black soot in the exhaust or tailpipe would also indicate an overly rich A/F mixture.

Part of 1 of 1: Adjusting your carburetor

1. Materials Needed.
2. Step 1: Remove engine air filter.
3. Step 2: Adjust the air fuel mixture.
4. Step 3: Observe the engine’s condition.
5. Step 4: Re-adjust air fuel mixture screws.
6. Step 5: Test the engine at idle and while revving.
7. Step 6: Locate the idle mixture screw.

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.

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.

keeping the engine under a light load (you will only be opening the throttle to 1/2 or so) If the needle is set too rich you will hear a sputtering like the choke is on and the acceleration will be slow. If the clip position is too lean the engine will sound quiet and have a “dead” feeling possibly hesitating.

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.

Set the idle speed screw(not L or H) so it is just able to idle by itself. This screw will have a “stop” it rests against. Now turn the L screw out until in decreases in rpm and then back in(very slowly) until it is at peak rpm. Adjust the H screw once more as above and it should be a very serviceable 2 stroke.

WD-40 Specialist® Carb/Throttle Body & Parts Cleaner with attachable precision straw is the only all-in-one carburetor cleaner spray you will need to clean your carburetor, throttle body, and unpainted metal parts. Then, the powerful cleaning spray blasts away the deposits and waste, leaving behind no residue.

While the crankcase tube is disconnected, you can attempt to spray WD-40 down into the tube. Leave the tube up to get the penetrator to the valve, thus cleaning it.

Aerosolized and applicable to nearly any carburetor, WD-40’s fast-acting carb cleaner uses a solvent formula to break away stubborn carbon contaminants, leaving you with a clean carburetor. WD-40’s blend of cleaners can be used on any unpainted metal parts.

1. Editor’s Pick: Chevron Techron Concentrate Plus Fuel System Cleaner.
2. Red Line Complete SI-1 Fuel System Cleaner (60103)
3. Royal Purple Max-Clean Fuel System Cleaner and Stabilizer (11722)
4. Liqui Moly Jectron Fuel Injection Cleaner.
5. Sea Foam Motor Treatment (SF-16)
6. Lucas Oil Deep Clean Fuel System Cleaner (10512)