Gastester

If you buy only one diagnostic instrument in your life this is it! Gastester is the world's most accurate and affordable exhaust gas analyzer. Gastester Digital measures the level of carbon monoxide (CO) in exhaust gas. Gastester Digital Instructions. Go Green with Gunson.

See Instructions Highlights

Why is measuring CO important? Variations in the fuel mixture affects power output, fuel consumption, and exhaust emissions, so the ability to measure fuel mixture is a critical step that was previously unavailable to the home mechanic. Gastester is indispensable when replacing or tweaking the existing carburetor, or when preparing for a state mandated emissions test. Gastester's accuracy rivals commercial units and there is no calibration gas to purchase and store. Included is a complete and comprehensive tuning and diagnostic instruction manual.

AEP's exclusive CO level to fuel mixture conversion chart converts Gastester's CO Level readout to a more performance oriented fuel mixture value. In addition, AEP's fuel mixture performance curve shows the fuel mixture range for maximum performance, low emissions, improved gas mileage or a balance.

Box received may differ from picture

Whether your passion is cars or motorcycles, Gunson has the tools that make engine tuning easy and straightforward. Gastester and Colortune help you tune like a pro by taking the guesswork out of engine tuning. Colortune is easy to use and gives you a visual indication of the air/fuel mixture based on the color of combustion which does not vary. Gastester measures percent carbon monoxide, the principle indicator of air/fuel mixture and engine efficiency but results may vary with ambient conditions. I supply a table, an AEP exclusive, that lets you convert from percent CO (useful for emissions testing) to air/fuel mixture.

If your engine has one carb per cylinder consider Colortune first. Whenever you are setting the fuel mixture you must measure the exhaust gas produced by the carb. This can be tricky on multi carb application since there are usually only two exhaust pipes. Some cars have exhaust header ports that you can connect Gastester to giving you the ability to measure and tune individual carbs. If you can see the top of the spark plug or can use a mirror to look down into the plug then Colortune will work well. If clearance is tight or line-of-sight is blocked then go with the Gastester.

To tune individual carbs with a Gastester you must be able to sniff the exhaust stream from either the tail pipe or from a port in the exhaust header. Some people are using a Riv-Nut kit available from Snap-on to create an exhaust port.

Check out the Maserati article where the author describes tuning individual carbs using a Gastester Digital. The author made adapters rather than using a Riv-Nut kit.

Tuning Resources

Rider magazine EGA Hooray

Exhaust Gas Analyzers Page 1 Page 2

Motorcycle Consumer News July 2002

British Car, 1993

Tuning Honda CBX 1 P2 P3

Tuning a Classic Mustang P1 P2 P3

Dune Buggies and Hot VWs, 1993 P1 P2 P3

Hot Rod, 1993

Tuning Honda CBX P1 P2 P3

Tuning a Classic Mustang P1 P2 P3

MB Clubgwagon Review

FJR Motorcycle Forum on Gastester

XKE lovers carb FAQ

Mobile Sources home page

How to create exhaust ports

Gastester info page

OBD II Theory

XKE lovers carb FAQ

Using Gas Analyzer Readings For Engine Diagnosis

Maserati Club Review

The ideal fuel ratio is about 14.7:1. A fuel injected vehicle under closed loop control will continuously adjust the fuel mixture to maintain the ideal fuel mixture. For carbureted vehicles the challenge is to reduce the fuel mixture so that gas is not wasted yet the engine is not damaged by a lean condition. Notice the range from 12.1:1 to 16.1 where an engine will run normally.

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).

Prices subject to change without notice

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