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Setting for Mixture Screw

joao44289

Enthusiast
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31
Location
Portugal
I'd like to know what's the correct setting for the mixture screw in the carburettor. I have a '79 R1123 with an 800-05 engine.
 

jjad

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1,379
Location
Herefordshire
I don't think there is a "one-size-fits-all" correct setting, as it will depend on your exact carburettor setup etc.

However, as an initial starting point, Malcolm's advice has been to screw it all the way in (gently) then turn it out by 1.5 to 2 turns.

This should provide an initial starting point for finer adjustment.

Personally, adjusting the carb is not something I've ever done: I leave that to the mechanics when I get the engine tuned at its annual MOT test.
 

Andrew4Renaults

Enthusiast
Messages
480
I don't think there is a "one-size-fits-all" correct setting, as it will depend on your exact carburettor setup etc.

However, as an initial starting point, Malcolm's advice has been to screw it all the way in (gently) then turn it out by 1.5 to 2 turns.

This should provide an initial starting point for finer adjustment.

Personally, adjusting the carb is not something I've ever done: I leave that to the mechanics when I get the engine tuned at its annual MOT test.

100% Agreed. G-E-N-T-L-Y wind in the mixture screw until the stop, then unwind it 1.5-2 turns, start the engine and wait for it to warm up and, once warm, start to wind OUT the mixture screw until the engine starts to "hunt". Then wind it in until the tick-over is even again. You may have to adjust the slow-running jet as well. Take the car for a run & see how it feels. A half-way decent "old school" garage will help you, and if you watch how they do it, you'll learn how to do it yourself next time!
 

Andrew4Renaults

Enthusiast
Messages
480
"Hunting" is when an engine doesn't settle to a happy tick-over. The revs go up & down and the car will not rev up properly. This is because the mixture is too weak and needs to be enriched to allow the engine to develop full power and idle properly.
 

joao44289

Enthusiast
Messages
31
Location
Portugal
"Hunting" is when an engine doesn't settle to a happy tick-over. The revs go up & down and the car will not rev up properly. This is because the mixture is too weak and needs to be enriched to allow the engine to develop full power and idle properly.

But if you're winding out the screw won't the mixture be richer (more fuel)?
 

Andrew4Renaults

Enthusiast
Messages
480
But if you're winding out the screw won't the mixture be richer (more fuel)?
Yes, sorry, I didn't explain that properly. I meant that as you screw the mixture screw IN the engine will begin to hunt, then you screw it OUT a little, until the engine sounds more "even". I'm sorry if I confused things! In many cases it's simply a matter of driving the car after setting it and then adjusting it again, until the car "feels" right.
 

joao44289

Enthusiast
Messages
31
Location
Portugal
100% Agreed. G-E-N-T-L-Y wind in the mixture screw until the stop, then unwind it 1.5-2 turns, start the engine and wait for it to warm up and, once warm, start to wind OUT the mixture screw until the engine starts to "hunt". Then wind it in until the tick-over is even again. You may have to adjust the slow-running jet as well. Take the car for a run & see how it feels. A half-way decent "old school" garage will help you, and if you watch how they do it, you'll learn how to do it yourself next time!
What counts as a turn? A 180º or 360º degree rotation?
 
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