Classic Audi » Technical » Mech/Tech » Engine » mixture screw fell off inside airbox

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Old 24-09-19, 02:59 PM   #1
a1quattro
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Default mixture screw fell off inside airbox

hi trying to get my 1984 2ltr coupe gt running , after recently giving her a full service including new fuel pump and filter ,cam belt water pump .Had played with mixture screw before all this work carried out , to get her threw mot , TODAY I couldn't seem to get 3mm allen key to do anything , so have just removed metering head lid off airbox only to find the mixture screw sat in bottom of airbox . . I spent 2hrs trying to wiggle it into postion onto end of allen key but I just cant seem to get it to screw back into bottom of metering head , very very fiddley , any suggestions
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Old 24-09-19, 06:24 PM   #2
tractor Dave
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You can use some grease on the screw to help it hold in position. Don't be tempted to turn the metering head up side down! It will be full of crud that will enter the system.
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Old 25-09-19, 07:10 AM   #3
larry49
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I would remove the fuel distributor leaving the lines attached, you will have a lot more room to see what you're doing. The screw has a very fine thread which you need to be careful not to cross thread.
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Old 25-09-19, 08:42 AM   #4
BackintheFold
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Quote:
Originally Posted by tractor Dave View Post
You can use some grease on the screw to help it hold in position. Don't be tempted to turn the metering head up side down! It will be full of crud that will enter the system.
+1 for "do NOT turn it upside down"
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Old 25-09-19, 01:15 PM   #5
Groundhog
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Why do you think the meter head should not be turned upside down? If a meter head is ‘full of crud’ then one has got some very serious problems with the fuel system. In fact if you are going to detach the meter head from the air flap housing I would strongly advise you do invert it in case the central plunger drops out. Also if the adjusting screw has fallen out simply putting it back is not enough of a fix, one needs to ascertain why it fell out in the first place. In the absence of any background information and without a visual inspection I would consider the option of a replacement air flap housing. In truth I am struggling to work out how it came to ‘fall out’.....interesting.
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Old 25-09-19, 01:26 PM   #6
BackintheFold
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Turned mine upside down once.
Didn’t like how it totally fukkced up the whole “being able to drive the car” thing.
Of course, YMMV....
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Old 25-09-19, 08:36 PM   #7
a1quattro
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The screw fell into airbox , as said before it was adjusted by mechanic [friend] at garage welst having mot , on way home it went ok but kept flooding up When pulling up and stalling , then very hard to restart . so I played with screw ,i didn't do my home work first . i.e I turned it a lot . not the fine adjustments req . any way it didn't make much difference . I decided to give car full service , New fuel pump,filter and accumilater, cambelt water pump , oil, filter, air filter and plugs , car starts but still not running nice so opend airfilter box only to find the mixture screw loose in box, I reckon id adjusted it to the point it just dropped out . I spent 2hrs with the metering head lid lifted but all still connected trying to wiggle the screw back into position and on to the 3mm allen key which I managed 3 times, but even with the flap arm pushing the screw into its postion I could not get it to wind back into the threaded hole welst turning allen key . it just dosnt seem to want to bite , . thread still looks good .
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Old 29-09-19, 01:47 PM   #8
a1quattro
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Default mixture screw re-fitted

update . after spending more than 3hrs trying to get the screw back into place I , decided it was impossible welst still fitted to car /pipes so marked with tape all the pipes off metering head . lifted unit from car onto work bench. removed 10mm bolt securing main butterfly flap .also removed the two brass scews /nuts 8mm holding the butterfly flap dampner .This enabled a beter view under the arm where the mixture screw should be attached stil fiddley but a dam sight easier than on car got it in , wound it all way anti-clockwise then counted how many full turns clockwise before risk of it dropping out . I made it 40 full turns , but would not ever go more than 35 . ive stuck a lable on airbox lid to remind me. I guess if car was running correctly there should never be any need to adjust to these limits . but at least we all now know don't turn more than 35 .
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Old 29-09-19, 03:49 PM   #9
larry49
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Now is the difficult part, setting the mixture. Someone else can probably tell you how many turns it should be in or out but when you get (it running) there the screw only needs to be turned 1/8 to 1/4 turn either way. I did this by ear to get the highest RPM at idle if the meter/bearings are clean and th
e flap set at the correct height.

Last edited by larry49; 29-09-19 at 03:58 PM.
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Old 29-09-19, 04:04 PM   #10
tractor Dave
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If you have a gas tester you can use that to set up. Warm up engine and make very minor adjustments until you get the correct co setting and smooth idle. Took a few goes with mine but now runs sweetly. My Gunston is 25 years old but still very accurate.
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