Greetings all Mk1 4x4 owners 
Here is the procedure for getting the automatic choke set up. It is a little fiddly and will probably not be right first time but this should get you to a reasonable point if it is not correct at the moment (i.e. it stalls easily when cold, or revs too high for too long before fully warming up).
You need to have the airbox / filter removed completely for this job...
1) First thing you need to do is make sure it is running ok when hot. If this is set wrong then the choke will be wrong as well. If it runs ok when hot then you can probably skip part 1! Might be worth checking anyway though.
You can only adjust idle mixture on these using the screw here:
turn this screw in (clockwise) until it begins to struggle to run. then turn back until the revs become stable. If the revs are too high then there is also an idle speed setting screw at the back of the carburettor (with a coil spring behind it). Turn this till the engine speed is as low as possible without running rough. You might need to switch between idle speed screw and idle mixture screw adjustment till you have the optimum smoothness / low engine speed setting.
NB if your idle speed won't drop check the accelerator cable isn't adjusted incorrectly (i.e. too tight and pulling slightly on the throttle even at idle).
Also please note this is not going to set it to perfect levels. You need an exhaust gas analyser or colour tune to know it is right for sure
2) Leave your engine to cool down completely - best to do this work in the winter or at least the worst conditions you are likely to come across wherever you live!
3)Loosen the following 3 screws which will allow you to rotate and set the choke position depending on how it is running.
Now only loosen these, do not remove them so you can quickly tighten it back when you have the correct position:
4) Now check the choke butterfly valve:
- If it is closed and fairly springy then it might be ok. Jump to step 5
- If it is not fully closed when the engine is cold then it will stall at every available opportunity Rotate the choke assembly till the choke butterfly is closed completely and partially tighten one of the screws to stop it from moving back.
NB the water pipes will all move with it - go with this for now because it can be adjusted later. Basically there is a spring inside which opens and closes when it changes temperature:
5) Start engine. It should run ok because you had set up the engine when hot.
It is possible that even with the choke fully closed engine speed might be too high or too low. If this is the case I will try to explain how to fix this (I forgot to take a picture of this sorry)...
At the front of the auto choke assembly just next to the water pipes there is a long screw coming off a throttle linkage lever on the side of the carburettor. This also sets engine speed but only when the choke is in use! Once warmed up the idle speed is set by the idle speed adjustment screw at the back of the carburettor (as I described in step 1). So set this if neccessary so revs are acceptable.
6) Now the clever bit. As the engine warms up the choke will try to open as it needs to put in less fuel. Now this is important... it will not change until the throttle is pressed so if you just leave it, the engine revs will go up and up and up. So...
Keep blipping the throttle every 30s / minute. The revs will eventually start to drop.
Case A:
If the revs stay high for too long, your choke is staying closed for too long. Re-adjust the choke butterfly by loosening the 3 screws off again (as per step 4) and blipping the throttle as you turn the choke assembly. When the engine is running right re-tighten to set position. Be quick though because the engine is continually warming up.
Case B:
The choke begins to open too soon and engine stalls / runs rough as it gets warmer. Again adjust the position by rotating the choke assembly until the revs come back up (but not too far).
TIP: keep checking how hot the choke assembly is as this will give you an idea of when the spring is going to begin to start changing the position of the choke butterfly valve.
This procedure may need repeating again (from a cold engine again) but you might get lucky and have it right first time
7) Final step once all is running ok is to re-set the position of the hot water pipes which go into the auto choke assembly. For example here mine are pointing upwards:
Loosen the 11mm hex head bolt. Water will begin to leak from this so be careful it might be hot (maybe don't do this right after turning the engine off for safety).
Rotate the pipes so they are completely horizontal again like this and re-tighten the bolt.
You might need to replace the gasket here (advised - mine leaked after adjustment) but don't over tighten this bolt. It will shear, they get very corroded and then you ruin the choke or give yourself a difficult job removing the remainder of the bolt!
These pipes must be level because:
- Pointing up, the airbox will not fit back on properly.
- Pointing down, the throttle linkage will foul on the bottom hot water pipe and you will be left with partial throttle (aka not enough power to get up a hill!)
I hope this is clear. I know there is a lot of detail here but I think this covers all the important information. You can see why most people replaced these with manual chokes right? :bang:
Hope it helps anyway. Let me know if anything needs clarification. I am a bit tired so might be a typo or 2 in there haha!
Si
Here is the procedure for getting the automatic choke set up. It is a little fiddly and will probably not be right first time but this should get you to a reasonable point if it is not correct at the moment (i.e. it stalls easily when cold, or revs too high for too long before fully warming up).
You need to have the airbox / filter removed completely for this job...
1) First thing you need to do is make sure it is running ok when hot. If this is set wrong then the choke will be wrong as well. If it runs ok when hot then you can probably skip part 1! Might be worth checking anyway though.
You can only adjust idle mixture on these using the screw here:
turn this screw in (clockwise) until it begins to struggle to run. then turn back until the revs become stable. If the revs are too high then there is also an idle speed setting screw at the back of the carburettor (with a coil spring behind it). Turn this till the engine speed is as low as possible without running rough. You might need to switch between idle speed screw and idle mixture screw adjustment till you have the optimum smoothness / low engine speed setting.
NB if your idle speed won't drop check the accelerator cable isn't adjusted incorrectly (i.e. too tight and pulling slightly on the throttle even at idle).
Also please note this is not going to set it to perfect levels. You need an exhaust gas analyser or colour tune to know it is right for sure
2) Leave your engine to cool down completely - best to do this work in the winter or at least the worst conditions you are likely to come across wherever you live!
3)Loosen the following 3 screws which will allow you to rotate and set the choke position depending on how it is running.
Now only loosen these, do not remove them so you can quickly tighten it back when you have the correct position:
4) Now check the choke butterfly valve:
- If it is closed and fairly springy then it might be ok. Jump to step 5
- If it is not fully closed when the engine is cold then it will stall at every available opportunity
Rotate the choke assembly till the choke butterfly is closed completely and partially tighten one of the screws to stop it from moving back.NB the water pipes will all move with it - go with this for now because it can be adjusted later. Basically there is a spring inside which opens and closes when it changes temperature:
5) Start engine. It should run ok because you had set up the engine when hot.
It is possible that even with the choke fully closed engine speed might be too high or too low. If this is the case I will try to explain how to fix this (I forgot to take a picture of this sorry
)...At the front of the auto choke assembly just next to the water pipes there is a long screw coming off a throttle linkage lever on the side of the carburettor. This also sets engine speed but only when the choke is in use! Once warmed up the idle speed is set by the idle speed adjustment screw at the back of the carburettor (as I described in step 1). So set this if neccessary so revs are acceptable.
6) Now the clever bit. As the engine warms up the choke will try to open as it needs to put in less fuel. Now this is important... it will not change until the throttle is pressed so if you just leave it, the engine revs will go up and up and up. So...
Keep blipping the throttle every 30s / minute. The revs will eventually start to drop.
Case A:
If the revs stay high for too long, your choke is staying closed for too long. Re-adjust the choke butterfly by loosening the 3 screws off again (as per step 4) and blipping the throttle as you turn the choke assembly. When the engine is running right re-tighten to set position. Be quick though because the engine is continually warming up.
Case B:
The choke begins to open too soon and engine stalls / runs rough as it gets warmer. Again adjust the position by rotating the choke assembly until the revs come back up (but not too far).
TIP: keep checking how hot the choke assembly is as this will give you an idea of when the spring is going to begin to start changing the position of the choke butterfly valve.
This procedure may need repeating again (from a cold engine again) but you might get lucky and have it right first time
7) Final step once all is running ok is to re-set the position of the hot water pipes which go into the auto choke assembly. For example here mine are pointing upwards:
Loosen the 11mm hex head bolt. Water will begin to leak from this so be careful it might be hot (maybe don't do this right after turning the engine off for safety).
Rotate the pipes so they are completely horizontal again like this and re-tighten the bolt.
You might need to replace the gasket here (advised - mine leaked after adjustment
) but don't over tighten this bolt. It will shear, they get very corroded and then you ruin the choke or give yourself a difficult job removing the remainder of the bolt!These pipes must be level because:
- Pointing up, the airbox will not fit back on properly.
- Pointing down, the throttle linkage will foul on the bottom hot water pipe and you will be left with partial throttle (aka not enough power to get up a hill!)
I hope this is clear. I know there is a lot of detail here but I think this covers all the important information. You can see why most people replaced these with manual chokes right? :bang:
Hope it helps anyway. Let me know if anything needs clarification. I am a bit tired so might be a typo or 2 in there haha!
Si
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