Gunson COLORTUNE G4074 User manual

FAULTCODE READER OBD11
COLORTUNE
GASTESTER
EEZIBLEED
PROFESSIONAL
PART NO G4074 / G4170 / G4171 / G4172
HANDBOOK

3
COLORTUNE
INDEX
Page
1.Application Details 4
2. Colortune Contents 5
3. General Precautions 6
4. How Colortune works 7
a. Combustion flame appearance
b.The Science
c.The practical details
5. Fitting Colortune to the engine 9
6. Simple engine tests with Colortune 10
7. Fuel system types 12
8. Engine fault finding with Colortune 16
9.Warranty 19

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1.Applications
Car and light commercial vehicles (Part No G4074)
Athread size of 14 mm has been used for nearly all cars and light vans produced in the last
50 years. One exception is the Ford SOHC Pinto engine (1970's) which was 18mm size
(adaptor available) and recently some vehicles have been introduced with smaller sizes due to
space restrictions on smaller 16 valve engines. Note:The hexagon size on 14mm plugs does vary
from 1980 onwards. A taper seat plug was introduced with a 16mm (5/8") hexagon (previously
13/16" or 20.6mm) and the 16mm hexagon size has also been used on flat seat varieties with a
revised body shape.
Motorcycles - 4 stroke (Part No G4170 / G4171 / G4172)
Athread sizeof 14 mm, 12mm or occasionally10mm, is used. The spark plug manufacturer’s
reference code helps with identification.These products has a smaller internal volume which
maintains the normal compression ratio and a higher heat range, more suited to high perform-
ance engines.
Motorcycles - 2 stroke
Athread size of 14 mm is almost universally used as there are no space restrictions caused by
valves.
Garden machinery and power plant engines
Athread size of 14 mm is generally used.

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2.Contents
The Colortune G4074
1. COLORTUNE plug-14mm size short reach with 16mm (5/8”) hexagonal body size.A hexagon
adaptor is provided to adapt to a 13/16” (20.6mm) plug spanner -also suitable for long reach
applications.
2. Solid cross section gas seal washer.
3. Extension H.T. lead incorporating an end suitable to connect either Champion or Continental
Bosch type suppressor caps (clip or thread)
4. Cleaning Brush
5.Viewerscope (two parts)
6. Instructions
The Motorcycle Colortune
G4170 - 14mm
G4171 - 12mm
G4172 - 10mm
1. COLORTUNE plug-Individually boxed with 10/12 or 14mm plug size, with reach with 16mm
(5/8”) hexagonal body size. A hexagon adaptor is provided to adapt to a 13/16” (20.6mm) plug
spanner -also suitable for long reach applications.
2. Solid cross section gas seal washer.
3. Extension H.T. lead incorporating an end suitable to connect either Champion or Continental
Bosch type suppressor caps (clip or thread).
4. Cleaning Brush
5.Viewerscope (two parts)
6. Instructions
Adaptors available for Colortune
10mm Part No 4055A
12mm Part No 4055B
14mm Part No 4055C
14mm Long Reach PartNo 4055D
18mm Part No 4055E
Colortune is available only in a short reach thread length but it may also be used in long reach
applications without any problem. It will still ignite the mixture and because it is only fitted for a
brief period therewill be no combustion carbon deposited on the exposed threads in the cylin-
der head.

3. General Precautions.
•Testing of vehicles is potentially hazardous.Take every precaution to avoid injury and ensure
that you have sufficient understanding of the task being undertaken. Seek advice or follow the
guidance of a comprehensive vehicle manual.
•Using this product involves working on a car while the engine is running. This is a potential
hazardand the user should take every precaution to avoid any possibility of damage or injury.
Never wear loose clothing that can catch in moving engine parts and always tie-up or cover
long hair. Do as much of the work as possible with the engine idle.
•Do not inhale exhaust gases - they are very poisonous. Always operate the vehicle in a well ven
tilated area.
•Always make sure the vehicle is in park (Automatic transmission) or neutral (manual
transmission) and that the parking brake is firmly set. Block the wheels as additional safeguard
if the vehicle is on sloping ground.
• Never lay metal tools on a vehicle battery. Always keep yourself and test equipment away
from moving or hot engine parts, remember that thermostatically controlled fans may
suddenly start with no warning. Treat high tension ignition components with respect, remem
bering that electrical shocks can cause involuntary movement which may result in secondary
injury.
• Never smokeor haveopen flames near the vehicle. Vapours from petrol or a charging battery
arehighlyflammable / explosive. Keep a suitable fire extinguisher handy. Use approved safety
equipment and eye protection where appropriate.
•Always turn ignition key OFF when connecting or disconnecting electrical components, unless
otherwise instructed. Never leave vehicle unattended while running tests.
• Keep children and pets awayfrom the vehicle while work is being carried out.
6

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4. How Colortune works
Understanding the principle by which COLORTUNE works helps in getting the best out of it.
That principle is commonly seen in action on paraffin heaters, gas cookers, or anywhere where a
fuel is burnt in air to produce heat or energy. Combustion at its most efficient produces a clear
blue flame, various other colours result from inefficient mixtures.
Inside an internal combustion engine those same coloured flames are present though not nor-
mally seen. With COLORTUNE fitted, in place of a sparking plug, the flame is visible through
the glass insulator and the fuel is ignited by a spark in the COLORTUNE.
This allows the user to obtain greatest engine efficiency by assessing the colour and appearance
of the flame and correcting any faults thus revealed.
Using the product could hardly be easier, fit it into a warm engine, in place of a spark plug, and
you are ready to begin.
COLORTUNE gives you a fascinating insight to the working of an engine without the usual com-
plexities of most other diagnostic equipment. It can provide a unique view of the behaviour of
the fuel system, in the individual cylinders, which no other equipment can do, saving in many
cases time, expense and a great deal of effort in fault diagnosis. A gas analyser gives an average
reading of all cylinders, and no diagnosis of faults or setting errors which affect mixture
distribution.
While working with this product be aware that:
• This product may be used at a wide range of engine speeds but should not be used in an
engine under load as overheating and product failure could occur. Take additional care when
using the product on an air cooled engine which has no fan assisted cooling. On these engines
limit the total test duration to 5 minutes and avoid extended running at high rpm.
• The viewerscope supplied with this product is made from a glass reinforced heat resistant
material but will be damaged by excessive heat before the Colortune plug. If this is damaged it
serves as a clear warning of overheating. Obtain a replacement and take more care to avoid
overheating. Discontinue use if the product plating is discoloured by heat or the glass / ceramic
shows signs of damage.
4.a. Combustion flame appearance
The general appearance of the combustion flame when viewed through COLORTUNE is as
follows:
YellowIndicates a fuel / air mixturewhich haveexcessive petrol content (rich).
Like a candle flame - producing more light but less heat.
Bunsen Blue Indicates a mixture which is correctly proportioned.
Whitish Blue Indicates a mixture which has less petrol content (lean)
Note: this colour is more easily seen at higher speeds.
At idle, engine instability and misfiring may occur before this weak mixture
and pale shade of blue is fully visible.
Therearesometimes exceptions to the above as petrol engines are imperfect machines, these
will be described later.

8
4.b.The Science
•The correctly proportioned mixture is - 14.7 parts of air by weight to 1 part of petrol
(hydrocarbon fuel).
•If there is perfect combustion, all the fuel will be burnt to produce carbon dioxide and water
with no carbon monoxide or unburnt fuel (hydrocarbons).
•The carbon in the fuel burns with oxygen in the air to produce carbon monoxide (CO), which
then burns with more oxygen to produce carbon dioxide (CO2)
•Hydrogen in the fuel burns with the oxygen in the air to produce water (H2O)
•Nitrogen in the air passes through to the exhaust with little reaction.
•When there is less air in the mixture, there is not enough oxygen to complete the burning
process so some carbon monoxide is not changed to carbon dioxide and hydrocarbons (unburnt
fuel) may be present in the exhaust.
•Carbon particles glow yellow in the combustion of a rich mixture and in severe cases you may
see black carbon smoke in the exhaust.
•When there is too much air in the mixture, it becomes more difficult to ignite, burns slower,
and is therefore less efficient.
•The diluted mixture burns with a pale flame.
•Misfiring may occur and hydrocarbon levels in the exhaust gas will rise.
•Carbon monoxide levels stay low because there is plenty of oxygen available to convert it to
carbon dioxide.
4.c.The practical details
• On an engine with one carburettor/single point injection, asingle Colortune plug will enable
the mixture to be observed in any cylinder for a quick check, or one cylinder at a time for a
morethorough evaluation of a multi-cylinder engine.
•Twin or multiple fuel systems can even be checked in this way (one cylinder at a time) but it is
time consuming and a comparison between cylinders at any instant is not possible.
•Multi-cylinder engines, particularly those with twin or multiple fuel systems are best tested
with a Colortune in each cylinder.
•Variations in mixture between the cylinders are easier to see and faults can be more easily
spotted and rectified.
•Nowhere is this better demonstrated than on high performance motorcycles - where accurate
calibration of at least eight settings on four individual carburettors is a highly skilled task, done
mainly by ear.
•Amoreaccurate setting can be achieved with Colortune in half the time normally taken.
NOTE:A multi-cylinder engine with a carburettor (or injector) to each cylinder and a single
exhaust system can not be thoroughly tested with a gas analyser at the tailpipe.The analyser
only gives an average fuel mixture indication for all cylinders and no warning of large mixture
variations due to setting errors or indication of other faults.
•Modern engines with multipoint injection systems, and earlier high performance car engines
with twin or multiple carburettors, have a lot in common with the example of the motorcycle
given previously.
•Colortune gives a marvellous insight to the inner workings of all these engines, so that errors
and faults can be easily spotted. Despite its simplicity, Colortune is an invaluable piece of equip-
ment for the amateur or the experienced technician.

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5. Fitting Colortune to the engine
1. Before fitting Colortune, start the engine and warm up to normal operating temperatures,
preferably by going for a short drive.
2.To assist with flame visibility, park your car in such a way that the engine is in the shade,
(or you may use the viewerscope attachment).
3. Stop the engine, take care to avoid hot engine parts and brush away any grit from around the
spark plug before removing it.
4. Fit the COLORTUNE in its place. Never over tighten COLORTUNE into the engine as an
adequate gas seal will be achieved even on taper seat applications with little more than the
equivalent of finger tightness.The rubber bush in a normal plug spanner will not retain the
Colortune as the ceramic is smaller.The HT adaptor lead may be attached and threaded
through the plug socket or viewerscope base to start the thread. A hexagon adaptor is sup
plied to adapt larger plug sockets to the smaller Colortune hexagon
5. If the plug recess is not easily accessible it is wise to apply high melting point grease to the
Colortune washer to help retain it.
6. Screw the plain end of COLORTUNE adaptor lead to the centre electrode of COLORTUNE.
Careshould be taken not to over-tighten it or bend the centre electrode.
7. Fit the lower half of the Viewerscope over the lead (if required) pushing the end down over
the hexagon. With the adaptor lead to one side, push the upper half of the Viewerscope into
the lower half in such a manner that the adaptor lead emerges from the slot in the upper half.
8. Plug the other end of the adaptor lead into the plug cap of the car's ignition system.The
adaptor is designed to fit both types of plug cap(with barethread or clip type fitting) and fits
most ignition systems.Try to keep the leads away from engine parts, particularly the exhaust
and rotating items.
9. Repeat the abovesteps if using morethan one Colortune.
10. Start the engine.All cylinders should now be firing regularly and the combustion flames
should be clearlyvisible, either directly or in the viewerscope mirror.
Avoid touching ignition parts when the engine is running remember ignition sparks can jump,
particularly if a connection is not secure.
Tightening torque nominal
10mm 0.20Nm - 1.2 ft-lb
12mm 0.24Nm - 1.4 ft-lb
14mm 0.28Nm - 1.6 ft-lb
Test Pressure Non Destructive 34 Bar 5000psi.
Destructive Test Pressure min. 95 Bar 12000psi.
See the following sections for adjustments and fault diagnosis

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6. Simple engine tests with Colortune.
Idle speed
With Colortune installed in a warm engine and the engine running at idle speed, a regular flash
of light, with a Bunsen blue flame, should be visible as the mixture is ignited in the cylinder. On
systems which have a slow running mixture adjustment, turn the adjustment to explore the
rangeof colour available. The position at which yellow disappears leaving only blue, is the rich-
est setting which should be used e.g. when setting mixture on a simple motorcycle carburettor
without an accelerator pump device. Engines before 1985 should be set halfway between the
point where yellow flame disappears (say 4.5%CO) and the point where engine speed falls slight-
ly (say 0.5%%CO). Engines produced since that date should idle at say 1%CO (almost at the
point whereidle speed falls).These leaner settings progressed with engine developments to give
economy with low exhaust emissions.
Oxygen Sensor MixtureControl
On engines which have oxygen sensor mixture control, no yellow flame should be visible.The
flame colour should be blue with a slight variation as the oxygen sensor continually trims the
mixture every two seconds approximately (more rapid at higher rpm). A yellow flame appearing
in some cylinders is an indication of an air leak into the other cylinder(s) or the exhaust mani-
fold.The sensor tries to compensate for the excessive oxygen level by increasing fuel input. (The
same can happen if one injector is faulty but symptoms may then be worse at higher engine
speeds, whereas an air leak has less of an effect when the throttle is opened.)
Part throttle
If the throttle is opened veryslowly until the engine is running at perhaps half of the maximum
rated speed, the blue flame should become slightly lighter. The lighter blue is due to a slightly
leaner mixture (less fuel) arranged to give improved economy at part throttle operation.
Note:At idle the same lean economical setting is difficult to achieve due to engine inefficiencies
at slowspeed with the throttle virtually closed.

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Full throttle
When maximum power is demanded (at full throttle position) it is normal to again have a
slightly richer mixture, at most engine speeds there will be a yellow flame. Engines with modern
electronic engine management systems which have more precise control would not usually give
ayellow flame at full throttle, except at times of rapid acceleration.
Rapid acceleration
When the engine is running slowly at idle and there is a sudden demand for power (throttle rap-
idly opened) this can cause an unstable condition and the engine may stall.A rich and easily
ignitable mixture helps to avoid this, so it is common to see a yellow combustion flame with
rapid engine acceleration. A special fitment may for example be provided on a carburettor to
achievethis extra fuel delivery - this is commonly called an accelerator pump.
Engines with modern electronic engine management systems which have more precise control
would give a very brief yellow flame which quickly reverts to blue. Less sophisticated systems
maygiveayellowflame throughout the period of acceleration.Very simple carburettors found
on small motorcycles and garden machinery may have no acceleration device on the carburet-
tor and will need a richer mixture setting at idle to avoid engine stalling or a “flat spot” during
rapid acceleration.
Cold starting
Arich and easily ignitable mixture is also provided for starting a cold engine. If a manual cold
startdevice (choke) is fitted, a yellow flame should be visible in Colortune when this is operated.
This applies with a hot or cold engine. If enrichment is byelectronic control unit (ECU) or auto-
choke, test for a yellow flame when the engine is cool / cold. Try to keep the test brief to avoid
carbon deposits on the Colortune glass.
Some exceptions to all the above conditions may be found, for example small engines used in
lawn mowers or chain saws may have simple fuel systems which are less able to provide the
ideal fuel / air mixture. Electric generators with speed governors do not experience rapid accel-
eration so should haveablue flame under all operating conditions.

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7. Fuel System types
The following description of fuel systems is intended purely to identify the various types which
may be encountered and to highlight the basic features. While this may be sufficient description
for some simple adjustments to be performed, a comprehensive vehicle manual or the General
Fuel System Manual should be referred to for further detailed information.
The information is in two main sections, one covering the various types of carburettor and the
second dealing with fuel injection systems. In each case the least complex systems are described
first for reasons of clarity.
NOTE: Many twin and multiple carburettors require flow balancing before mixture is set - see
the end of this section
Abasic Carburettor fuel system
1.There are four basic elements to a simple “fixed choke” carburettor which might be fitted to
garden machinery or small power plant engines
2.A throttle to open or restrict the main passage of fuel / air mixture to the engine, this usually
has an adjustable throttle stop to control idle speed.
3.A float and valve arrangement to maintain a steady fuel supply level (or a sensitive pressure
regulating diaphragm)
4.A slow speed fuel discharge and adjustment (idle jet and idle mixture screw) this is found
close to the engine mounting flange and the throttle plate.The throttle uncovers extra
passages (progression holes) for feeding fuel as it begins to open.
5.A high speed fuel feed and adjustment (main jet and main mixture screw) normally located
closer to the inlet air cleaner mounting flange.The main fuel discharge feeds into a venturi
shape, whose restriction (a fixed sizechoke) gives a low pressure to pull the fuel in.
6. Note: a cold start device is also sometimes called a choke - it also gives a restriction to draw
in extra fuel.
Carburettor fuel systems as fitted to motorcycles
1.Variable chokecarburettor.This usuallyhas the same parts as described in items 1-3 for the
basic fixed choke carburettor but the main discharge has fine tapered needle in a jet to meter
the fuel accurately. The variable choke size is formed by a rising piston arrangement attached to
aflexible diaphragm. When the throttle is opened, the engine draws in more air and the
diaphragm pulls the piston and the needle further open, maintaining a constant low pressure
(constant depression) in the carburetter.This gives precision control of the air and fuel over a
rangeof conditions. Enrichment for acceleration conditions may be provided with a separate
pump device or bycontrolling the rate at which the piston rises. Needle / jet calibration size
controls mixture except at low speed / light load which is governed by the adjustable idle mix-
ture control.
2. Slide type carburettor. The slide carburettor has been used on motorcycles and other small
engines for very many years. Fuel feed is from a chamber with float and needle valve and an idle
fuel system is provided with an adjustable mixture screw.There are no progression holes in the
idle system as the throttle plate is replaced by the slide which gives this carburettor its name.

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The slide is attached to a needle running in a jet in a similar way to the variable choke carburet-
tor but this does not give a constant depression as the slide position is governed by the throttle
position selected at the time, not by a diaphragm.
Mixture is governed by the shaped bottom of the slide at lower speeds/light loads, the needle
taper and position at mid speeds and the main jet size at all engine speeds when on full throttle.
Carburettor fuel systems fitted to car engines
Fixed chokecarburettors.
These are broadly similar to the basic carburettor fuel system described except no adjustment
is normally provided for the fuel fed by the main jet system.
More sophisticated idle and main circuits are used, with additional fuel feed circuits.Also there
are air jets and emulsion tubes which provide a graduated addition of air bubbles (emulsion) to
give greater control of fuel flow characteristics.
Idle speed adjustment is normally by a throttle stop screw, but sometimes this is locked and an
adjustable throttle by-pass passage is used.
This type may have two fixed choke carburettors combined in one casting to provide either -
Atwin choke carburettor where both throttles open simultaneously -generally for improved
power output (two twin choke carburettors may be fitted to a high performance four cylinder
engine).
Atwin choke (progressive) carburettor where one choke is used for most low speed driving and
the other opens in addition for high speeds. This gives improved economy and smooth engine
response
Variable chokecarburettors.
These have some similarity to motorcycle variable choke carburettors but a separate idle circuit
is not usually provided. Two basic types are used with control of the air valve being either
diaphragm (Stromberg/CD) or piston in cylinder type (SU).
Aconstant depression (low pressure) is maintained on a tapered needle and jet system which is
attached to the air valve/carburettor piston.This air valve rises as the throttle is opened and
then at full throttle it will continue to rise further as the engine speed also increases.This gives
accurate mixture control over the whole range of operation. Enrichment for acceleration condi-
tions is provided by controlling the rate, at which the air valve rises, with an oil damper, (the oil
may requiretopping up regularly).
The fuel needle is machined with a veryaccurate taper, individuallyselected for each engine
design. Spring loaded types of needle are more accurate when new but they rub against the jet
giving errors when worn (e.g. over 50,000 miles 80,000 Km). Appearance of the combustion
flame will be rich at the operating conditions wherethe needle is worn (usually idle / part
throttle). If the mixture has been adjusted to normal at idle, weak mixtures will then occur
under acceleration.
Fuel injection systems
Drawing it in with air under lowpressure).The amount of fuel should be in proportion generally
with the amount of air going into the engine, but this is adjusted slightly for economy at part
throttle, higher power at full throttle and other less significant reasons.A three dimensional map
of the requirements, for a specific engine, is drawn and it is then the job of the injection control
system to satisfy this requirement. Determination of the quantity of air going into the engine is
itself a difficult task under conditions of varying temperature, varying pressure, and with
extreme disruption to the flow caused by valves opening and closing at an incredible rate. Some
systems attempt to measure flow directly with a moving vane in the air flow, or a hot wire sys-
tem which senses the cooling effect of the air flow. Others use a prediction from the throttle
position, engine rpm and the manifold pressure. All have various means of compensating for
engine and air temperature, atmospheric pressure etc. Early systems use more mechanical
parts, later systems still require a mechanical pump to maintain a steady high pressure but

14
control is almost entirely electronic.
Fuel injection systems with adjustable idle mixture
Single point injection.
This system has one injector and one throttle plate through which all air and fuel passes into the
engine manifold. Despite this simplicity, the same control systems are required to achieve accu-
rate fuel metering. Idle mixture and idle speed, are the two adjustments that may be provided
on early systems.
Multipoint injection with one throttle plate.
Separate injectors are placed close to the inlet valves rather than in the main throttle body.The
manifold system is designed with a suitable inlet tract length to enhance engine performance.
This feeds from a larger chamber and throttle body which does not have the same dimensional
restrictions as the single point system because it feeds air only. Idle mixture and idle speed, are
the two adjustments that may be provided on early systems.
Multipoint injection multiple throttle.
Some early systems which were mainly mechanical in operation had this arrangement.
Balancing the air flow through each throttle plate is crucial to effective operation. Injectors are
set to deliver equal quantities of fuel and any error in air flow then has a dramatic effect on mix-
ture.Testing and fine tuning of the balance between throttles requires patience even with a
Colortune in each cylinder. It is almost impossible without Colortune. A Lucas system of this
type was fitted to a few high specification vehicles in the early 70's and a few other road vehicles
and racing systems fit this description.
Fuel injection systems with oxygen sensor feedback
The development of sophisticated electronic control systems plus a robust exhaust oxygen sen-
sor allowed the three way exhaust catalyst to be introduced.This had a dramatic effect on
exhaust emissions and was introduced into most vehicle markets from the early 1990's.
The oxygen sensor gives no output when there is oxygen present in the exhaust (both sides of
the sensor are exposed to oxygen) and it gives an output (usually 1.0 volts) when there is no
oxygen present in the exhaust (when there is a difference across the sensor). It is therefore an
excellent detector of small percentages of oxygen and the electronic control unit (ECU) is able
to continually adjust above and below the point at which the sensor has an output. The ability of
the ECU to learn and adjust the programmed mapof information stored in its memory, adds a
further precision of control.
With this type of injection system thereis little or no facility for adjustment, (except perhaps
fuel pump pressure, selection of different settings for different octane fuels etc).When there are
no faults present the performance is generally very good under all operating conditions, but
even minor faults may have an exaggerated effect. Colortune can provide a unique view of the
behaviour of the fuel injection system, in the individual cylinders, which no other equipment can
do, saving in many cases time, expense and a great deal of effort in fault diagnosis.
Fortunately,manysystems also havethe facility for a limited amount of self diagnosis, and give
fault code information in the form of a blink code (a number indicated by a flashing led) or
more complex forms of data transmission.This may pinpoint the problem or give some guide to
the area that requires investigation. Often the information requires further analysis as the sys-

15
tem does not recognize mechanical problems only the effect on electronic items and will show
for example a lambda (oxygen) sensor or lambda control system fault in the case of inlet or
exhaust manifold air leaks.
Multiple, twin and twin choke carburettors.
Multiple throttle body injection.
On any system that has multiple throttles, it is important to synchronize the action of these
before setting mixture controls. This ensures that the system is balanced, but more importantly
it aids accurate mixture setting.
The procedure is usually a basic mechanical setup of the following procedure. Release the link-
age; adjust throttle stops to achieve identical air flow, clamp linkage. Check that throttles begin
to open simultaneously when operated by the actual accelerator cable or rod mechanism, (not
some other part of the linkage).
Atwin chokecarburettor that has both throttle plates in one casting does not usually progres-
sive opening.
Fixed choke carburetors
If twotwin chokecarburettors are used the linkage between these must be set to achieve a
synchronized opening.

16
8. Engine fault finding with Colortune
As Colortune allows you to view the burning of the fuel air mixture, most of the faults observed
during its use will be mixture / fuel system related. However, there are other faults which affect
efficient combustion and these will also be easier to diagnose. For example, an engine misfire
which occurs despite the mixture being correct can be identified as an ignition or compression
fault.
The following information gives a basic guide but operator experience and other published infor-
mation will be invaluable in identifying the causes of observed combustion problems.These will
vary with specific fuel systems and other engine equipment.
Always determine the extent of the problem, for example:
Is the fault affecting all cylinders, multiple cylinders or just one cylinder?
In the case of multiple cylinders what is common to these?
(Two together may have a head gasket leak between them or be fed by one of twin carburet-
tors).
Is the fault mainly at idle speed, low throttle or wider throttle opening?
AT IDLE SPEED
Symptoms Fault details for different fuel systems
Blue combustion flame is
not achievable when adjust-
ing idle mixture
Fixed Choke - Blocked idle air jet / idle jet loose
Variable Choke - Wear on needle / jet
Injection System -Senses high air flow, air flow device faulty / vane
sticking, throttle position sensor / switch. Cold start device or
temp sensor
Yellow combustion flame is
not available when adjusting
idle mixture
All systems - Manifold air leak. Check other cylinders to help pin-
point position of leak.
Fixed Choke -Blocked idle jet / idle air jet loose
Variable Choke-Needle loose or shoulder set low, sticking air
valve.
Injection System - Air leak or idle air valve, MAP sensor fault
(detects low air / manifold pressure).
Blue flame turns yellow after
aprolonged idle
Fixed Choke and Variable Choke - Leaking float chamber needle
valve.
Variable choke - overheating causes rich idle. Check inlet manifold
insulator block fitting.
Blue combustion flame is
not constant, intermittent
yellow at all or most settings
Fixed Choke-Blocked idle air jet gives erratic idle fuel discharge.
Float level high gives main circuit "drip" feed
Variable Choke - Float level high. Advanced ignition timing pro-
ducing engine instability.
Injection System - Oxygen sensor response slow
Blue combustion flame is
not visible (non adjustable
systems)
Injection System - Oxygen sensor / connection or control failure.
Air leak to exhaust manifold or to inlet manifold if confined to
most cylinders but not all cylinders.

17
ABOVE IDLE SPEED
RAPID THROTTLE OPENING
Symptoms Fault details for different fuel systems
Yellow Flame at
1000-1700rpm
Fixed Choke or carburettor with separate idle circuit - restricted
idle air bleed
Variable choke - Worn metering needle/jet
Yellow Flame
1200 and above
Variable choke - Hole in diaphragm.
Manifold air leak results in a rich setting to compensate for a
weak idle (rich setting then affects whole operating range)
All carburettors - Float chamber level high
Intermittent yellow
Flame1200 - 1500rpm
Fixed Choke - Main circuit feeding early, Float chamber level too
high. (Lower by 2mm approx) The fuel drips (not spray) if it feeds
too early Variable Choke - Sticky air valve / carburettor piston.
Yellowappears at high rpm
only
Fixed Choke-Main circuit feeding early, Float chamber level too
high. (Lower by 2mm approx) The fuel drips (not spray) if it feeds
too earlyVariable Choke - Sticky air valve / carburettor piston.
Light blue flame
engine unstable 1000-2000
rpm
Blocked main jet or water in the fuel system.
No yellow flame visible at
any speed or flat spot in
acceleration followed by
little yellow flame
Fixed choke - Accelerator pump not working.
Observe for fuel discharge into choke when throttle is opened
(engine stopped).
Variable choke - Oil damper needs top up
Fuel Injection - MAP sensor or Throttle Position Sensor fault.
Faulty idle switch

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9.Warranty
The Tool Connection Limited has made every effort to ensure that this
product is of the highest quality and value to the customer.
However, The Tool Connection accepts no responsibility for any
consequential loss or damage arising from the use of this product.
All technical enquiries regarding this product should be made to The Tool
Connection Technical Service Department: ++44 (0) 1926 818181
or returned to:
The Tool Connection,
Kineton Road,
Southam,
Warwickshire
CV47 0DR
When sending goods for service or repair, please give full details of faults
requiring attention and proof of purchase for warranty claims.
This Warranty does not affect the Statutory Rights of the user.

Gunson 05/2005

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