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CARB ; MIXTURE ADJUSTMENT

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WARNING

TAKE CARE WHEN WORKING WITH PETROL ;  USE COMMON SENSE AND IF YOU FEEL IT IS BEYOND YOUR CAPABILITIES

THEN PLEASE SEEK COMPETENT HELP

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SYMPTOM ; CAR RUNS BUT ONLY WITH THE CHOKE ON

POSSIBLE CAUSE ; FUEL STARVATION

Requiring the choke to be constantly on is a classic symptom of fuel starvation .
When you pull the choke on it moves the main jet away from the needle.
Since the needle is tapered this allows more fuel to flow past and into the engine .

{ CAUSE }

The carb is adjusted too weak

{ SOLUTION }

ADJUST THE CARB

Remember to have a fire extinguisher handy when working with petrol  

Get the engine started and FULLY warmed up .

Stop engine .

Remove the air filter assembly

Make sure the choke cable is FULLY pushed in inside the car .
Slacken of the choke cable at the carb and remove the little choke clamping screw and pull choke cable from carb end only .
A wee tip for you ; Get a length of the rubber petrol pipe about 8 inches long and soften one end in hot water then push over the throttle adjusting screw

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Mark one of the flats on the LARGE mixture adjusting nut at the bottom of the carb with a magic marker .

Screw the adjusting nut fully in by using your fingers { count the number of flats on the nut from where it is set now to the fully up position }.

Screw back out about 18 flats { 3 full turns out }

At this setting it will probably be a little weak         

This should be a starting position .

The mixture is usually correct any place around 21 to 24 flats although carbs do differ 

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Start the engine and , using the end of the rubber hose , just screw the throttle adjuster screw in till you get a very FAST tickover .

Leave running till the engine is fully warmed up

Adjust {You can often just use your fingers only} the LARGE mixture adjusting nut at the carb bottom IN to weaken and OUT to richen .

Looking at the pic of the carb from the angle above  ;

It is turn nut to the LEFT to RICHEN and to the RIGHT to WEAKEN

Looking at the the carb from the top downwards   ;

It is turn nut CLOCKWISE to RICHEN and ANTICLOCKWISE to WEAKEN

Adjust it SLOWLY a flat at a time and you will come to a point where the engine revs will not be clean and it will be running poorly .

YOU ARE LOOKING TO FIND THE POINT WHERE THE ENGINE RUNS FASTEST AND EVENLY .

Adjust back to marked flat and continue the other way till the same thing happens .
Adjust SLOWLY back and forth till the engine is at its fastest smooth running .

Readjust the tickover down to an acceptable level .

STOP engine . 

Go to the following page to

SETUP the CHOKE then RE-ADJUST the MIXTURE IF REQUIRED 

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You can also check the mixture if your carb has a lifting pin as per the following link ;

SU Carb HS2 type  ;  Mixture Checking by Lifting Pin
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Remember to have a fire extinguisher handy when working with petrol  

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