You may of heard the phrase 'Tuning by ear’ which basically means adjusting the ignition and carburetor until the engine sounds right. It's a phrase you can forget, because tuning by ear is about as accurate as setting a quartz watch with a sundial - it just ain't on! To do it correctly, you're going to need some instruments. So stop guessing your fuel mixture and start tuning like a pro with Gastester the world's most affordable and accurate and exhaust gas analyzer.

Use Gastester to measure and set your engine’s fuel mixture just like professional engine tuners. Gastester brings professional tuning capability to the home market at a price that is affordable, and Gastester’s accuracy rivals commercial units costing several thousand dollars.

Tuning with Gastester is easy. Just stick the probe up the exhaust pipe and take a carbon monoxide (CO) reading. Then check the reading against manufacturers specs, your own custom specs, or your state mandated emission limits and adjust the mixture screw until you get the reading you want. AEP takes the mystery out of tuning with our exclusive air/fuel ratio chart and power curve. The power curve tells you what the fuel mixture should be for maximum power while the air/fuel ratio chart converts Gastester’s CO reading to a more meaningful fuel mixture value.

So why is proper tuning important? All that unburned fuel is wasted money and toxic pollutants. You can get better performance and lower emissions if you take the time to properly tune your vehicle. Gastester gives you the information you need to tune your engine for the way you drive. With Gastester you can be a power tuner and drive a clean mean machine.

Ask yourself these questions:

Do you tune your vehicle by ear?
Do you know what your air/fuel ratio is, or are you just guessing?
Do your eyes water when you're near the tail pipe?
Do you want increased performance and better fuel mileage?
Do you need to pass your state's emissions test?

Gastester lets you tune your engine for the way you drive.

The air/fuel ratio can be set for maximum power or minimum fuel consumption, or a balance of the two. Included with Gastester is AEP's air/fuel ratio conversion chart (available only from AEP) showing the air/fuel ratio for any given level of CO. This chart makes tuning easy. With Gastester and the chart you can select the air/fuel ratio you want by simply adjusting the mixture screw until Gastester displays the level of CO corresponding to the desired air/fuel ratio.

CO is the principle indicator of fuel mixture.

Gastester works on the 'hot wire' or thermal conductivity principle. According to this principle, the thermal conductivity of a gas depends on the particular mixture of gases present, and is largely independent of gas temperature. In practice the thermal conductivity of exhaust gas varies only with the amount of carbon dioxide (CO2) that is present. Gastester measures the thermal conductivity of the exhaust gas, and therefore measures its carbon dioxide content. Since there is a inverse relationship between carbon dioxide and carbon monoxide (CO), as CO2 goes up CO goes down and vice versa. Gastester senses CO2 but displays CO. The 'correct' CO level will generally result in improved performance, better fuel consumption, and cleaner more environmentally friendly exhaust emissions. The secret to Gastester's success is the patented sensor that provides accurate CO reading at an affordable price.

How to prepare for your state's emission test.

Gastester only measures CO, but the levels of hydrocarbons (HC) and oxides of nitrogen (NOx), --the other pollutants typically measured -- can be inferred from the CO level.

Since the CO/HC/NOx relationship is constant and predictable, you simply adjust the fuel mixture until you get a CO level that is less than or equal to your state's CO limit for your make and model car. If your car is in tune and set up to manufacturers specs you can be fairly confident that the hydrocarbon and NOx levels are within limits. If possible give yourself a cushion of at least .5% CO to account for Gastester's accuracy. Note: the level of NOx is also affected by timing advance. The greater the timing advance the higher the NOx level.

A well maintained car is likely to pass state emissions testing without difficulty, so regular attention to maintenance is recommended. This will also result in more satisfying and more reliable driving, and will also be cheaper in the long run. The recommended order of maintenance/emissions testing preparation is:

ensure the air filter is clean or replace.
ensure valve clearances are correctly set.
service ignition system/plug leads/set points (if any)
set carburetor air balance where multiple carburetors are used.
set air/fuel mixture strength.
change the engine oil (hydrocarbons accumulate in the oil).

Carbon Monoxide, chemical CO, is a very poisonous gas that is present in small quantities in exhaust gas. The level of CO in the exhaust gas indicates whether the engine is running rich or weak. For this reason, car manufacturers now use CO as an accurate indicator of whether the jets of the carburetor are correctly adjusted.

Hydrocarbons (HC) is the name given to a group of chemicals that are found in gas. Some of the fuel passes through the engine unburned and can be detected in the exhaust gas. The amount of HC in the exhaust gas is generally very low, and therefore, is measured in parts per million (PPM). Note that 1% is the same as 10,000 PPM. The presence of excessive HC in an engine in good condition, are typically 100-300 PPM. For an engine in very bad condition, for instance, one cylinder not firing at all, the level can be as high as 20,000 PPM. A wide range of faults can cause excessive HC in the exhaust, but common causes are: faulty spark plugs and ignition system and faulty ignition timing. There is no simple equipment available for measuring HC. However, an engine that is well maintained should be able to pass state emissions test if you do all the little things.

Gastester is very easy to use.

Just let it warm up for about ten minutes, set the display to 2% CO (this is the CO reference point) and then insert the probe in the exhaust pipe. Unlike the expensive models no special calibration gas is needed because Gastester uses air as its calibration standard.

Instruction Highlights

Use the rotary calibration control to carefully reset to the CALIBRATE reading of 2.0% CO. The instrument displays two decimal places on the CO range as a result of the high resolution display. The last decimal place is insignificant and when setting to 2% in air the user should not be concerned if 2.00% exactly can not be obtained.

Having set the CALIBRATE condition do not move the instrument, or move to a different location during subsequent CO tests.

When the probe is subsequently inserted into the exhaust pipe, the display of the instrument may increase or fall from the CALIBRATE condition, depending on whether the exhaust has more than, or less than, 2% CO.

Ensure that the engine is set to the idle RPM stated by the manufacturer. Now insert the probe into the vehicle’s exhaust pipe to a minimum of 3/4 of its length, i.e. 8” or 20cm. In order for the automatic water drain to function, the probe pipe should fall continuously from the exhaust end to the inlet end to allow water droplets to run down. Otherwise the water will collect at the lowest point and will have to be drained manually.

Wait for a period of 15 seconds for the meter to respond and a further 1 minute to stabilize (the reading may overshoot before returning to a steady value, particularly during the initial measurement).

Make a note of the reading and observe the display for a further one or two minutes to ensure that the reading is indeed steady and within tolerance for the vehicle concerned. If the reading is not between the manufacturer’s recommended maximum and minimum, or is not below that specified as a legal requirement, then adjustment of the carburetor or fuel injection system will be required.

If adjustment is required, make a small alteration to the mixture screw, and correct the idle speed by adjusting the idle speed screw (or throttle bypass screw if fitted - see figure 6 & 9). Do this repeatedly in small increments, under these conditions the reading should stabilize in less than one minute at each mixture setting.

When the test is complete REMOVE THE EXHAUST PROBE PIPE and switch off the engine.

Allow a period of at least 5 minutes or at least 10 minutes in still air conditions with little breeze, for air to purge the exhaust from the instrument. This period in air with power on cleans the sensor before storage and also allows a check to ensure the display returns close to the 2% setting indicating that there has been little drift in calibration.

Special Note: A final reading of 1.8% in air for example would suggest that the last exhaust measurement was approx 0.2% lower than the displayed level. While this is perfectly acceptable when setting to approx 3% to ensure that a vehicle passes a 4.5% maximum legal requirement, it does represent a more significant error if setting to a manufacturer’s recommended 0.5% CO. On occasions it may be necessary to repeat a test if calibration drift is excessive (drift is reduced by keeping test duration short and allowing a long warm up).

A port for Gastester

Prices subject to change without notice

John Abbott
2574 nw 29th Drive, Boca Raton FL 33434