Preparations Before Use; Instructions For Use - Gunson GASTESTER G4125 Manual

4. Preparations
before use
• Any service and maintenance such as air filter renewal, tappet adjustment, carburettor
maintenance, ignition maintenance including ignition timing, should be carried out before
setting the carburettor or fuel injection mixture adjustment. Petrol mixture setting should be
the final adjustment in any engine tuning work.
• Carbon monoxide is an extremely poisonous gas and any work on the car with the engine
running should therefore be carried out in the open air. Take care not to breathe in gases
when using the gas tester.
• Study the workshop manual for the particular vehicle or engine to identify the correct
adjustment screws that control the mixture strength and the idle speed. Make a note of the
initial position of the adjustments before commencing work.
• The car should be fully up to running temperature before connecting the Gastester. In order
to achieve full temperature the vehicle should be driven till oil, water and the exhaust system
are all fully up to temperature.
• Have to hand the correct tools for making the necessary adjustments. If the manual
recommends a CO level at a particular engine speed, then a tachometer should be used.
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Note: Place the main body of the instrument away from the exhaust gas stream. Clean air
is required in the internal reference cell for accurate readings.
1. Place the Gastester on a convenient flat stationary surface close to the vehicle's exhaust pipe
outlet. Switch off the engine temporarily while making connections. Connect the red (+) and
black (-) clips to the vehicle's 12 V battery or convenient positive and earth (ground) points.
(Do not use this Gastester with 6v or 24v batteries.)
2. Fit the probe to the Gastester but do not fit to the exhaust at this stage.
3. Allow a minimum period of eight minutes with the instrument probe in fresh air. Set the
calibration control to achieve 2.0% on the CO range and observe the display for a further two
minutes minimum to ensure that the reading has stabilized.
Note: if it has not stabilised allow a further two minutes before attempting to measure
exhaust CO level.
4. During the warm up period check and adjust the engine idle RPM if required.
5. Check the calibrated reading is still set at 2.0% in fresh air, once set and stable do not mover
the Gastester.
6. Insert the probe into the exhaust pipe a minimum 8" (20cm), the display will now show the
percentage level of CO in the exhaust. If the display remains at 2.0% then the percentage
level is 2% and happens to match the percentage level found in fresh air
Note: 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.
7. After insertion of the pipe wait for a period of 15 seconds for the meter to respond and a
further 1 minute to stabilise (the reading may overshoot before returning to a steady value,
particularly during the initial measurement).
8. Make a note of the reading and observe the display for a further one or two minute to confirm
that the reading is steady and within tolerance for the vehicle concerned. If the reading is
outside the manufacturer's recommended limits, or is not below that specified as a legal
requirement, then adjustment of the carburettor or fuel injection system will be required.
9. If adjustment is required, make a small alteration to the mixture screw, and correct the idle
speed after each adjustment. After each adjustment wait for at least one minute for the
reading to stabilise.
10. When the test is complete remove the exhaust probe and switch off the engine. Leave the
Gastester connected to the vehicle's battery and allow a period of at least 10 minutes for fresh
air to purge the exhaust from the instrument. This period in fresh air with the 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.
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% 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 longer warm up).

5. Instructions for use

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