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S-Series Tuning Techniques
Always make sure that ignition components are in good condition and that the engine oil level and the coolant level are correct. Remember general engine condition and valve clearances can affect engine tune. It will be helpful if you are a novice to firstly obtain a workshop manual to help identify components and simplify assembly & disassembly.
Before doing any tuning work, you must make sure that all the vacuum pipes are in good condition and connected correctly.
Check the pipes on the air temp control valve are correctly orientated. The pipe stub with the small hole connects to the manifold.
Check crankcase breathers are not blocked and there are no air leaks. Easy way to check for air leaks is to remove the small pipe to the air filter & put your finger over the end, then remove the large pipe that connects to the carburettor then blow into that pipe, if the pipe holds pressure all is well, then take your finger off of the small pipe to release the pressure otherwise you will get a mouth full of gunk.
Check that the air temperature control flap is not sticking and that the diaphragm is working correctly when a vacuum is applied.
Check air filter is serviceable (If in doubt fit new) and the hot air duct is connected and not split.
Remove vacuum switch and test diaphragm for any air leaks. (If you suck on the vacuum connection you should NOT be able to suck air through)
It is always a good idea to remove the ORFCO valve before attempting any carburettor tuning, and check that it is properly closed. Then refit the valve and leave it disconnected. Tape up the wires!!
Ensure full throttle is obtainable from inside the car and that there is enough free play to give movement at the lost motion lever. Adjust cable and lost motion link accordingly. (This check is done with engine warm).
If you do not have a gas analyser then you cannot expect to get the air fuel mixture correct but if you are careful you may get it close. Remove carburettor dash pot and clean with carburettor cleaner, observe the position of the main jet inside the carburettor venturi, screw the mixture screw until the top of the jet is level with the brass bush then screw the screw in one full turn. This should give a slightly rich mixture in most cases. Refit the dashpot.
Top up carburettor damper with engine oil.
Take the car on a 4-mile road test, immediately on return set the idle speed to around 850rpm
If you are a novice or doing a tune for the first time you may find it useful at this point to unplug the stepper motor to prevent throttle jacking taking place. (When ECU controls idle speed) This is not normal tuning procedure, so if you are confident you would recognise throttle jacking if it occurred ignore this part.
To set mixture, slowly screw the mixture screw out until the engine just slows slightly (if engine speeds up just carry on until engine slows) then screw the mixture screw back in until the engine runs its fastest this will probably be no more than ¼ of a turn.
If you disconnected the stepper motor then reconnect it now. Set the idle speed to 800rpm.
Pull off the coolant sensor plug; using the fast idle adjuster set the fast idle speed to 1100rpm. Reconnect the sensor plug.
Reset idle speed if necessary.
If cooling fan cuts in whilst setting the carburettor, wait for it to go off then run engine at 2000rpm for 20 seconds then continue.
Regards Gary
Before doing any tuning work, you must make sure that all the vacuum pipes are in good condition and connected correctly.
Check the pipes on the air temp control valve are correctly orientated. The pipe stub with the small hole connects to the manifold.
Check crankcase breathers are not blocked and there are no air leaks. Easy way to check for air leaks is to remove the small pipe to the air filter & put your finger over the end, then remove the large pipe that connects to the carburettor then blow into that pipe, if the pipe holds pressure all is well, then take your finger off of the small pipe to release the pressure otherwise you will get a mouth full of gunk.
Check that the air temperature control flap is not sticking and that the diaphragm is working correctly when a vacuum is applied.
Check air filter is serviceable (If in doubt fit new) and the hot air duct is connected and not split.
Remove vacuum switch and test diaphragm for any air leaks. (If you suck on the vacuum connection you should NOT be able to suck air through)
It is always a good idea to remove the ORFCO valve before attempting any carburettor tuning, and check that it is properly closed. Then refit the valve and leave it disconnected. Tape up the wires!!
Ensure full throttle is obtainable from inside the car and that there is enough free play to give movement at the lost motion lever. Adjust cable and lost motion link accordingly. (This check is done with engine warm).
If you do not have a gas analyser then you cannot expect to get the air fuel mixture correct but if you are careful you may get it close. Remove carburettor dash pot and clean with carburettor cleaner, observe the position of the main jet inside the carburettor venturi, screw the mixture screw until the top of the jet is level with the brass bush then screw the screw in one full turn. This should give a slightly rich mixture in most cases. Refit the dashpot.
Top up carburettor damper with engine oil.
Take the car on a 4-mile road test, immediately on return set the idle speed to around 850rpm
If you are a novice or doing a tune for the first time you may find it useful at this point to unplug the stepper motor to prevent throttle jacking taking place. (When ECU controls idle speed) This is not normal tuning procedure, so if you are confident you would recognise throttle jacking if it occurred ignore this part.
To set mixture, slowly screw the mixture screw out until the engine just slows slightly (if engine speeds up just carry on until engine slows) then screw the mixture screw back in until the engine runs its fastest this will probably be no more than ¼ of a turn.
If you disconnected the stepper motor then reconnect it now. Set the idle speed to 800rpm.
Pull off the coolant sensor plug; using the fast idle adjuster set the fast idle speed to 1100rpm. Reconnect the sensor plug.
Reset idle speed if necessary.
If cooling fan cuts in whilst setting the carburettor, wait for it to go off then run engine at 2000rpm for 20 seconds then continue.
Regards Gary
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