Gunson G4125 Handbook

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GASTESTER

Handbook G4125

www.gunson.co.uk

33

GASTESTER

Digital Exhaust CO Analyser with Pulse Pump

INDEX Page

1. Contents 4

2. Assembly 4

3. Descriptions and controls 5

4. Preparations before use 5

5. Instructions for use 6

6. Further information 7

7. Common problems 8

8. Multiple carburettors 9

9. Carburettor Adjustments – General Information 10

10. Single Fixed Venture Type 12

11. Single Variable Venture Type 12

12. Idle Adjustment 13

13. Technical Specification 18

14. General Warning 18

15. Warranty 19

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Gastester is an exhaust gas analyzer that works on the “Hot Wire” or “Thermal
Conductivity principle. According to this principle, the thermal conductivity of
exhaust gas varies in proportion to the amount of carbon monoxide present.

CO Function

Calibrated range: 0-10% CO

(indicates uncalibrated to 20% C)

Accuracy: +/- 0.5% CO Typical

(Throughout the indicated range 0.5% CO to 6.5% CO)

1. Contents

1. Gastester instrument including collector box and pulse pump/water trap assembly

2. Metal exhaust probe with retaining springs

3. Flexible pipes (3)

4. Instruction handbook

2. Assembly

• Warming the various pipes will assist assembly. Only the connection to the vented
collector box inlet needs to be pressed fully home.

• Press the shortest pipe onto the lower boss of the Pulse Pump/Water Trap as shown
in the diagram Figure 1. This is the automatic water drain.

• Connect the other plastic pipe between the Pulse Pump outlet and the collector box
inlet. (This connection is intentionally vented at the inlet boss). The connection to the
collector box inlet needs to be pressed fully home.

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3. Descriptions & Controls

DISPLAY This is calibrated in volume percent carbon monoxide (CO%)

CALIBRATION CONTROL This is used to set the reading of the display to show 2.0% at

the start of the tests, before the probe is inserted into the exhaust pipe. (NB: The
calibrate position represents what the instrument should register when the probe is in the
air. It is coincidental that air should measure the same as exhaust gas with 2% CO).
When the probe is subsequently inserted into the exhaust pipe, the display of the
instrument may increase or fall from the calibrate condition.

TWO CORE CABLE WITH CLIPS (for connecting to the car battery)

EXHAUST PROBE. The metal pipe is for insertion into the exhaust pipe and is retained

in position by the metal springs which press against the inside of the exhaust pipe.

NB In use the pipe from the exhaust probe should slope down continuously to the
Pulse Pump/Water Trap so that water runs down and may be automatically
expelled from the drain pipe.

4. Preparations before use

• Any service maintenance such as air filter renewal, tappet adjustment, carburetor maintenance,
ignition maintenance including ignition timing, should be carried out before setting the carburetor
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 car (or consult the information given later in this
booklet) 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 thoroughly warm before the tests begin. It is not enough to leave the car to
warm while parked. The car should be taken for a drive and the tests not commenced until
water temperature, exhaust system and engine are running at normal 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 would be an
advantage.

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5. Instructions for use

Ensure that the car is thoroughly warm as mentioned above, that it is parked in a
convenient position in the open air, with the handbrake applied.

NB: THE INSTRUMENT SHOULD NOT BE PLACED DIRECTLY IN THE EXHAUST
STREAM. CLEAN AIR IS REQUIRED IN THE REFERENCE CELL FOR ACCURATE
READINGS.

1. Place the Gastester Professional on a convenient flat 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 (Do not use

this Gastester with 6v or 24v batteries)

2. The probe should be fitted to the instrument but do not insert the exhaust probe into
the exhaust pipe at this stage

3. Restart the engine and allow a minimum period of eight minutes with the instrument
probe in the air. Set the calibration control to achieve 2% on the CO range and
observe the display for a further 2 minutes minimum to ensure that the reading
has stabilized.

4. IMPORTANT if it has not stabilized allow a further 2 minutes before attempting to
measure exhaust CO level.

5. During the warm up period other ranges will give accurate readings and it is therefore
useful to check and adjust engine idle RPM.

6. Switch to the CO range with the probe in air.

Do not insert the exhaust probe into the exhaust pipe at this stage

7. 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.

8. 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.

9. 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.

10. 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).

11. 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 carburettor or fuel injection system will be required.

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