Carburetor mixture adjustment

[Janko]

Hello,

on my 1992 GTL (zenith 28) there is a problem. Yesterday i had a MOT. The mixture was too rich and the MOT guy adjusted the air/fuel mixture spining this screw:



The MOT passed, but my car is not drivable as before. It doesn't feel right, it hesitates a little when i want to accelerate. I am very sad, because i had relaible setting before and very good consumption (5-6l/100km). When it's cold it's even worse. I have to use choke for a longer time and when i release it, the cars hesitates when i want to accelerate, until it gets hot. Before i used choke for a very short time and there was very little hesistation. I think the engine is getting too much air. I tried spinning the adjusment screw, but i can't get it right, it's never the same as before.. I have no idea which settings was before. So i was wondering two questions:

If you spin it clockwise, this means more air or more gas?

Is there a factory setting? Counting spins from the end?

Thank you for your help

Janko

 

[Janko]

I did a little google-ing and found this;

http://users.atw.hu/renault4/KARB_ALLIT.jpg

I turned the screw all the way in and set it to 1.5 counts out. It's much better now..

 

[tim1casa]

I had the same happen to me in Spain after the garage had it in for the MOT. After the engine had been running terribly for several months, missing, stopping on tick over, and only having any umpph when you pulled the choke out slightly, I eventually had to adjust the mixture screw.

 

[angel]

Do you only have to be OK on CO emissions to pass the MOT, or do they also check HC (hydrocarbons) emissions?

 

[orsome]

Do you only have to be OK on CO emissions to pass the MOT, or do they also check HC (hydrocarbons) emissions?

Janko, you have only too "fresh" car, we have here in Finland(i do not know if it is a EU regulation or not), here 1979 and newer cars have to pass emissions testing, mine is 1977 model, luckily.
I also have this Z28IF "friend" and have been struggling with ist choke, i gad changed a new inlet valve but it seem to sit too low(too low fuel level), i changed back to old and original valve .Measurements showed for the new valve 0,8mm too low position, io it vas so much higher from planed surface to the ball tip and had 0,5mm bigger radius setting on the neck to be screwed in.Took even of all copper washers.Then i planed the carb joint matching the suction header, sand paper towards a plain glass.
Now it is far better, i can even use choke.

 

[Tripyrenees]

I am having problems with black soot coming out and the adjuster (fuel/air) is not really doing a lot. I changed the various gaskets in the carb and cleaned it well but nothing much has changed.

 

[mojobaby]

My 1980 GTL failed her MOT yesterday because the CO levels were too high.
The maximum allowed is 4.5% and she had 6,8%

The carburetor is Zenith 28 with the single air/fuel screw.

Like Janko, I don't know whether to turn the screw clockwise or anti-clockwise to reduce the fuel.

And like Tripyrenees I can turn the screw in and out and there is no difference in the sound of the engine. My exhaust has a lot of black soot and my plugs are also black with soot.

Can that little screw be worn?

 

[Paul Narramore]

Without firm evidence (well it worked for some political parties) a mixture screw has a tapered point which when screw inwards, restricted the fuel, so inwards weakens it, outwards enriches it. (I defy you to prove me wrong ;-)

 

[mr-reno-139]

Mr Narromar
You are at 237 post already well done
And yes you are correct btw
For testing purpose screw in as far as possible, but needs to idle well enough for testing
Then set where it runs best after test ☺

 

[mojobaby]

Thank you both I'll give it a shot.

 

[Bobble]

Screw it all the way in then approx one and a half turns out should be about right may need to adjust very slightly either way for your own preference.

 

[mojobaby]

Thanks Bobbie, I had it 3 turns out as per the Heynes and then one more for luck

No wonder my exhaust was black