Running rich

[crankedup5]

My 1923 vintage car, recently purchased , is runnng rich. The car bumbles along OK but looking at the spark plugs they are well sooted up with black carbon The engine is running its original Zenith
carb’ which only offers changing the jet size to ease the issue. Almost impossible to find correct jets.
Would it be worthwhile using hotter running spark plugs to stop them up ? I have thought about swapping the carb for an SU abut no idea which model SU would suit the engine. Thanks for any inputs.

[v8250]

You may like to talk to Burlen Fuels, also to the club technical team of your make/type of car.

https://zenithcarb.co.uk/shop?_gl=1*5naf7x*_ga*MTE...

[crankedup5]

Thanks for link that’s great.
I do belong to the ‘Swift club’ but unfortunately so very few active members and the tech’ man hasn’t as yet been able to help much. In fairness I did say to him some months back I would run and fettle the carb’ as best as I could. Car has been in my garage ever since for various reasons.
Thanks for link again.

[OutInTheShed]

How complicated are the jets?
Maybe a bloke with a lathe could make some?
Maybe you could drill and tap a spare jet so that a 'common' jet like a Dellorto could be screwed in?

Alternatively I've heard of people putting a bit of wire in the jet to reduce the orifice.

[crankedup5]

OutInTheShed said:

How complicated are the jets?
Maybe a bloke with a lathe could make some?
Maybe you could drill and tap a spare jet so that a 'common' jet like a Dellorto could be screwed in?

Alternatively I've heard of people putting a bit of wire in the jet to reduce the orifice.

Thanks for suggestions, the jets, there are just two, are very simple brass screw in items with the tiny orifice. I guess the jet size is letting too much petrol through. If Burlen can’t assist then maybe I could find an engineer to ‘fill’ the orifice and then drill out smaller.

[Gazzone]

You can solder up the orifice and redrill to a smaller size.

[Ozzer2006]

Burlen fuels were excellent and helping me get very rare parts for my zenith. Definitely speak to them

[austin]

Austin 7s originally had Zenith carbs, if you are insistent on keeping it I would post in the A7 Friends forum asking about them.

On all my 7s we have fitted SUs as they are much easier to run with. If it's stopping you from using the car I'd do that. Can always swap it back if needed.

[crankedup5]

Thanks to all contributors.
I am a member of two A7 clubs so I will contact them for a chat, and I will contact Burlen as well.
Hopefully resolve the issue.

[ingenieur]

Sometimes it isn't running rich though. If your air intake has problems you may be getting less air into the engine than you should and that makes a rich mixture but it isn't because of the fuelling setup. I would have a look through all of the intake to see if there is any build up of debris anywhere inside it. If you had a mouse in there he might have made a bed for himself and taken up 1/2 the volume with his bedding.

[spoodler]

Befopre going to the trouble of changing the carb, I'd check the ignition is all working as well as it should, if it's delivering a less healthy spark (or at the wrong time) it could give the symptons of running rich.
As said above, if jets aren't available, your existing jet could be blocked and redrilled to a smaller size... used to do this motorcycle jets with a chemical metal type mix when I was young and impecunious.

[crankedup5]

Again some good suggestions as to where to look for a fix, or in my case for somebody to look for me. The engine was re-built ten years ago or so along with some ancillaries. Of course it’s possible the carb missed out.

[Lotobear]

I'm not too familiar with Zenith carbs, however float heights are also worth checking and as others have said if needs be the jets can be silver soldered and re sized with jet drills (I had this done when having mine set up on a RR as the jet orifices were out of spec)

[crankedup5]

The true value of PH, a font of knowledge and good advise. Thanks chaps.