CARB ; SOME FAULTS and SOLUTIONS
CARB ; SOME FAULTS AND REMEDIES
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Some of the Common things to go wrong with the SU carb are ;
{ A } Blockage of the floatbowl with fine rust particles from the tank
{ B} Wrong setting of the mixture adjuster at the bottom of the carb.
{ The previous owner might have been trying to adjust the mixture and set it wrong }.
{ C } Setting the gap on the choke lever before the engine is fully warmed up and tickover is set .
{ D } Faulty Float or the Needle in the float chamber not sealing off the petrol inlet and letting the carb flood a little .
{ E } VERY worn throttle butterfly valve spindle leak .
{ F } Lack of oil in the dashpot
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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 1 }
The carb is adjusted too weak
{ SOLUTION 1 }
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 { about 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
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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 ANTI CLOCKWISE to WEAKEN .
Adjust the nut CLOCKWISE SLOWLY , a flat at a time , counting the amount of flats and you will come to a point where the engine revs will be running faster .
Adjust back a flat at a time { counting the number of flats } until the engine revs slows or gets uneven .
Adjust SLOWLY back and forth till the engine is at its fastest smooth running .
YOU ARE LOOKING TO FIND THE POINT WHERE THE ENGINE RUNS FASTEST AND EVENLY .
Readjust the tickover down to an acceptable level .
STOP engine .
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SET THE CHOKE GAP
SU CARB showing CHOKE SETUP & BREATHER TUBE
Stick the choke cable back on carb and fit through clamping screw BUT do not tighten screw at this point.
Get feeler gauges and set for 40 thou .
Measure the gap between the screw underneath the choke arm and the lever and adjust so that it is a nice sliding fit { take care that the feeler gauges are 90 degrees to the arm or you will get a false reading }
Tighten up locking screw on choke cable .
Recheck gap .
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Refit the air filter assembly .
Because you have refitted the air filter assembly you will have to fine tune the mixture just a little .
Restart engine { you should be able to start it without putting your feet anywhere near the throttle } and once again using the end of the rubber hose , just screw the throttle adjuster screw in till you get a very FAST tickover .
Try weakening the mixture by one flat and see if it runs slightly faster / smoother .
If it does , then leave it there .
If not then reset back one flat and try one flat the other way
It should not be far away from your original marker { probably ¼ to half a flat weaker required }
Get a helper to sit in the car and press the clutch pedal right down and you can now reset tickover so that with the clutch depressed it is still ticking over nicely .
You can also check the mixture if your carb has a lifting pin as per the following link ;
http://www.gowerlee.dircon.co.uk/Tips.htm
STOP engine .
Mark the flat on the bottom adjuster nut with a different colour marker , and you will be able to fine tune or put it back to the same spot .
NOTE ; You will have to wait till the engine is stone cold to try out the choke .
All you should need to do is pull out the choke fully and turn the key without touching the throttle with your foot .
Remember to have a fire extinguisher handy when working with petrol
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{ CAUSE 2 }
Dirt in the carb { usually fine rust particles from the petrol tank }
{ SOLUTION 2 }
Remove the carb and check for sediment in the bottom of the floatbowl
Remember to have a fire extinguisher handy when working with petrol
I would be inclined to remove the carb and check for rusty deposits at the bottom of the floatbowl ,
Before you do this I would advise you to get a new carb floatbowl gasket because they sometimes tear when being removed .
Remove the air filter assembly
Remove the choke cable { Take care not to lose the wee choke cable clamp }
Remove the petrol hose and overflow hose { If fitted }
Remove the carb and work on it well away from the car
Do not be apprehensive about the carb clean
The only parts you need to touch are the floatbowl lid and the suction chamber .
When you do get the floatbowl lid and float off , just get a very thin screwdriver / needle and agitate the brown gunge in the bottom and empty out the bigger parts .
Fill the float bowl with fresh petrol about a third full , swirl around and empty out .
Repeat procedure until petrol runs clear .
Remove the suction chamber complete with piston and needle and you are left with this
Quarter fill the floatbowl with petrol then GENTLY blow through a small tube into the hole where the needle goes . This will flush any sediment back into the float bowl where you can repeat
Quote:
Fill the float bowl with fresh petrol about a third full , swirl around and empty out . Repeat procedure until petrol runs clear .
Refit the floatbowl assembly .
Refit the suction chamber complete with piston and needle and top up with oil .
Remember to have a fire extinguisher handy when working with petrol
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{ CAUSE 3 }
Restricted flow from the wee plastic fuel feed pipe from the carb floatbowl to the mainjet
{ SOLUTION 3 }
Check the pipe for kinking / flattening ;
Check the end of the pipe where it disappears into the bottom of the floatbowl .
There is a Seal shaped like a sharp edged ” O “ ring in there which sometimes blocks the tube .
For simplicity I will just call it a Seal in the following
If it is not leaking at the brass nut at the bottom of the floatbowl then I would leave well enough alone BUT if you feel competent enough or the problem of not enough petrol to the carb is still there then the following might help .
CARB ; FLOATBOWL ; FEEDPIPE SEAL RENEWAL
Remember to have a fire extinguisher handy when working with petrol
BEST TO REMOVE THE CARB so you can see inside the threaded hole in the bottom of the floatbowl .
{ I WOULD NOT RECOMMEND THE FOLLOWING UNLESS YOU ARE COMPETENT AND HAVE A WEE BIT FINESSE / SAVVY ;
You can still inspect it without removing the carb by removing the passenger side access panel and you will see the brass feed nut . Be aware that petrol will drain from the floatbowl when you do the following
ONLY DO ABOVE INSITU ON A STONE COLD ENGINE }
BEST TO REMOVE THE CARB
Gently grip the outside spring and pull back .
Slacken the nut and you will be able to gently pull it out .
Now this is the part where you need to take great care .
GENTLY pull the nylon pipe out of the hole keeping it inline and do not twist or crush the pipe as you will have to buy a very expensive whole unit .
As you can see from the picture there is the nut , a small washer to compress the Seal , and the Seal itself .
PARTS
The Seal ;
The following photo was copied from minispares.com
http://www.minispares.com/product/Classic/Fuel/Carburetors/Spares/AUD2194.aspx
Often the Seal remains inside the hole and has to be dug out with a pin .
Take care not to drop the Seal or the small washer .
Inspect the Seal for cuts or crushing and fit a new Seal .
Check inside the hole for little bits of cut Seal and remove as required .
Assembly is the reversal of extraction ; Gently grip the outside spring and pull back , refit the nut , steel washer and new Seal .
Just set the assembly up as in the last pic by keeping pressure on the nut so that the end of the tube goes into the hole first . This should ensure that the Seal stays on the tube .
Again take extreme care not to twist or crush the nylon pipe .
Tighten the nut but do not over tighten { You can Nip it up a little more if there is a slight leak }
Remember to have a fire extinguisher handy when working with petrol
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{ CAUSE 4 }
VERY BADLY WORN THROTTLE BUTTERFLY VALVE SPINDLE
{ SOLUTION 4 }
Replace or refurbish carb
Remember to have a fire extinguisher handy when working with petrol
Following was originally posted by Reliant World forum member chgperformance ;
Had a 93 robin LX in the other day. Woldnt run right in the mornings. Weve known the guy with this reliant for a long time so decided to have the carb off for a jolly good clean up. Upon inspection, the main jet was very was as was the needle. THey were changed for new items. The robin would then refuse to tickover without choke. I then used carb cleaner and sprayed around the carb mountings etc to find there was an air leak. THe carb gaskets were replaced where it meets the heat exchanger but still ran with the need for choke. I used car cleaner again but this time with a pipe on the end and aimed it directly at the throttle butterfly spindle. To my amazment it did affect it. I then cleaned and stripped a second hand SU, fitted the new main jet to it along with the needle and hey presto. Robin now runs properly again with some small tweeks here and there on mixture etc.
My conclusion being, the main jet/needle as it wore allowed the mixture to richen up to compensate for the worn spindle bush. When i changed the main jet/needle, it metered the fuel properly and thus leaned it out because of the air leak around the spindle bush.
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NEEDLE SIZES ; INFO ONLY
AEB is the Yellow top needle
AAT is the needle usual for most other engines
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SU carb parts available at ;
Remember to have a fire extinguisher handy when working with petrol
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{ CAUSE 5 }
VERY BADLY BLOCKED INLINE FUEL FILTER
{ SOLUTION 5 }
REMOVE THE STANDARD INLINE FUEL FILTER and
REPLACE WITH A LARGE CLEAR FILTER
Check the inline fuel filter located in the petrol pipe near the petrol tank .
This is usually found inside the clear plastic pipe at or near the part of the chassis which is at a 45 degree angle in front of the petrol tank and back axle
If still fitted , remove the inline bronze filter located in the petrol pipe line just in front of the petrol tank and fit a large clear plastic inline fuel filter or other suitable filter .
Click HERE for pics showing detailed location point of inline filter
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{ CAUSE 6 }
Air leaks at gaskets
{ SOLUTION 6 }
Fit new Gaskets or tighten nuts up
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NOTE ;
I am not saying that the stuff I have written above is all that could be wrong ,
but it is a start and hopefully some of the info might be of benefit to you .
ONCE AGAIN I WARN YOU TO TAKE CARE WHEN WORKING WITH PETROL ;
USE COMMON SENSE AND IF YOU FEEL IT IS BEYOND YOUR CAPABILITIES
THEN PLEASE SEEK COMPETENT HELP
Remember to have a fire extinguisher handy when working with petrol