General Petrol Slurper Uno 60

[Brymak]

My 1986 Uno 60S Solex carb is only returning around 8km per litre approx 22 mpg. Sometimes something in the carb sticks and motor will only run on full throttle. I have found that I can temporarily fix this by manually pumping on the accelerator pump linkage, so maybe the fault lies there? I had the carb professionally rebuilt about a year ago. Any ideas folk?

 

[Chas Uno]

A couple of things spring to mind here.

I had a similar problem on a Ford Cortina fitted with a twin choke carburetor, though in that case it would only run and have any power at full throttle. All that was wrong was that the vacuum pipe from the carburetor to distributor had perished at one end causing the distributor to stick at one end of the advance/ retard curve as a result. This meant that the car only had power at full throttle and no-where else. Replacing the pipe made it work as normal again.

As your problem comes and goes, it sounds more like a sticking float inside the carburetor. If the float sticks open the carburetor floods, and therefore makes a mixture so rich that it will only run with the throttle butteryfly(s) wide open.

Are you getting a strong smell of petrol when the problem occurs?

And perhaps by manually pumping the accelerator pump linkage is somehow clearing the excess fuel and making the float sit correctly? Hard to say, but you may need to strip the carburetor down again to investigate.

Either way, you certainly shouldn't be getting 22mpg from a Uno. Even the turbo boys would find that excessive!

 

[alexGS]

I think the 'turbo boys' would find anything less than 35mpg excessive! Mine's very economical anyway...

A blocked main jet in the primary system will cause the engine to only run at 'full throttle', since then the engine is running on the secondary system. However, this usually causes lean running, not rich, since the secondary is usually set up for running at high RPM - high airflow volume. Low airflow would hence give less fuel than usual (carburettor works by airflow - the more airflow, the more petrol drawn out of the jets.)

My Uno 60 with Solex carb was tremendously fuel-efficient, so the carburettor is not fundamentally 'thirsty'.

It sounds to me a bit like you have a split accelerator pump diaphragm, allowing excess fuel to find its way into the venturi.

Also I think Chas is onto the right track. If the float level is wrong (or there is dirt under the needle valve seat) then the fuel level in the carburettor becomes too high. Fuel starts to slop over directly into the venturi. I know that mine used to do this after stopping the engine, making it difficult to restart, as the heat from the engine would soak into the carburettor and cause the fuel level to rise.

Check, with the air cleaner off, that you can see/hear a squirt of petrol as you operate the accelerator linkage. That should eliminate the possibility of a split accel. pump diaphragm. After that, I'd be taking apart the carburettor, cleaning it out, blowing it out with compressed air, and setting the float level according to the Haynes manual measurement (usually 7mm from the float top surface to the cover underside, as I recall).

-Alex