Technical Fuel mixture

[Peterg]

Hi Guys
I fitted a new exhaust system a few weeks ago and see that there is a lot of black soot on the tail pipe.
The car is not pumping out smoke so I guess the fuel mixture is too rich.
Can anyone tell me how to reduce it.
I am guessing it is blocked in with a plug as I cannot see any screw to adjust on the carb.
1992 60S 1108CC
Thanks
Pete

 

[M@nticore]

yo, you can adjust your idle mixture at a screw at the footbase of your carb. in= lean out= rich, but the only way you can adjust your air/fuel ratio for upper throttle levels is to adjust your float level or change the sizes of your main jets. hope this helps. check workshop manual for correct size jet & correct float level mm seting.

 

[sumplug]

float level will not change fuel/air mix.all it does is keep the chamber at the right level during running.overfueling is caused by;-
incorrect mixture settings.
wrong grade plugs.
air filter/housing dirty or blocked.
worn carb or jets worn.
timing out.
blocked breather system
worn engine.

 

[Chas Uno]

If most of your driving is over short journeys and/ or round town (meaning the choke has probably been used a lot), then black soot in the tailpipe is quite normal.

Take it on a long run, keep the engine at operating temperature and cruise at motorway speeds and then check. You'll probably find that the the exhaust will be a lot cleaner with less soot.

If there is no visible black smoke from the exhaust (black = unburnt fuel/ rich mixture, blue = burnt oil, white = water/ headgasket failure), and fuel consumption is approximately normal then it's unlikely that your car is running rich.

The mixture can be adjusted at the carburetor base scew, BUT, it ONLY adjusts the IDLE mixture. At partial to full throttle openings the mixture is controlled by the jets inside the carburetor, which are non-adjustable. You can change some of them though.

Before adjusting the carburetor, you should always check the rest of the engine first. If the air filter is dirty, or engine breather blocked you can get a rich mixture. Also check the ignition timing and spark plug condition.

Otherwise I suspect your Uno is fine and you have nothing to worry about!

 

[Peterg]

Thanks guys
Yeah I use my uno for short journeys so that would explain why the tail pipe is all sooted up.
Pete

 

[M@nticore]

yo, sumplug. your float level does have an influnce on the air/fuel mixture. go get yourself a book called carburettors for dumies and check it out.

 

[(CZ)enda]

I am finding it somewhat surprising that 1992 1.1 60 is equipped with a carb?
Thought they were delivered with Bosch Mono Jetronic by then ?

 

[Peterg]

Can confirm it has a carb not fuel injection.
Pete

 

[Louie Bee]

Hi all,

The Porter Manual says (for the UK) Unos after June 92 were fitted with Bosch Mono Jetronic injection. Maybe Peterg’s Uno was first registered prior to this.

In other parts of the world, The Uno was available with a carb for many more years

Regards,