Zenith carb mixture adjustment

Could someone please tell me where the mixture adjustment screw is located please on my Zenith carb?

The Haynes manual is somewhat vague and I'm buggered if I can see it!

It's running very lean so I need to get the old boy running spot on again!

It's on the engine side of the carb near the base. Awkward to see from the wing side.
If you look at the carb from the wing (6 o'clock) the mixture screw is 11 o'clock near the base.

Hope this helps.

Been trying to adjust mine today as was running rich. Now I think it's a touch lean as the exhaust is popping a little on over-run .

i had a zenith in my 2a, some had a black plastic shield protecting the screw from being turned easily, i would take mine off strip the whole thing down clean it put it back together, turn the mixture screw in as far as it would go without damaging anything and then turn it out 3 turns, then start from there adjusting lean or richer.

i ended up taking the zenith off and put a Holden Stromberg bxv carby on, it has the right jetting, and it sure made a big difference to the pick up and smooth running.

Tony.

Thats great thanks folks Mine is running very lean with the pop on overrun too and needs to be a little richer and it was the MOT tester that told me that lol

Na the mot man is using modern equipment for a modern motor. The 2.25 was always designed to run a bit rich. Exhaust pop is normal. I think I did a post on this ages ago but am on my phone so cant do a link. Try and search maybe. Ive forgotten what the procedure is.
Ive got the zenith 36iv service guide here too which is useful. I did try and attach it but its too big. Ill have a scan again on setting the mix

I've just been going with this on mine today.

One little wrinkle made the mixture adjustment screw do absolutely nothing - and that was that, on removing the screw, the groove down it was COMPLETELY blocked with old varnishey muddy gunk.

MOT fail on mine was very low CO (~0.15%) and slightly too high HC (~1400ppm), which wasn't a surprise, since the lack of any kind of idle meant that I had to leave the choke on a whiff - but it ran beautifully.

The idle screw (throttle stop) wouldn't screw in enough to idle, so I've moved the locking collar to the back. Idle as low as it'll go without dying, and mix set 1.5 turns out, then out until it sounds nicer.

It's now idling and pulling reasonably smoothly, but has gained a bit of a "fluff" accelerating hard in third. It doesn't seem to start quite as easily as it did, either.

We'll see what it comes up to on the MOT machine, and what we can get it to.

ronsealdeath said:

Ive got the zenith 36iv service guide here too which is useful. I did try and attach it but its too big. Ill have a scan again on setting the mix

Click to expand...

I'd really like to see that - I'm happy to put it on Dropbox or similar, if we can figure a way to get it to me.

Anyone remember the Gunstone colour tune plugs? A spark plug with a glass top in it so you could see the combustion and set the mix to a fine Bunsen blue. I used to have one back in the days before ECMs and fuel injectors. Worked fine on my old VW and 240 Volvo.

TooMany2cvs said:

I'd really like to see that - I'm happy to put it on Dropbox or similar, if we can figure a way to get it to me.

Click to expand...

Will have a try later buddy

OK, try this

https://drive.google.com/file/d/0BzmF8nvZr-z_R0ItQVlKR01iQ1k/view?usp=sharing

Should work and take you to the bulletin jobby. Good document and useful for me when rebuilding and troubleshooting my Zenith. It was so useful, I bought a Weber 34ich

That worked, ta.

Thanks for that Handy document!