You are forgetting how the "choke" on a SU carb works. None of them have a true choke plate to close/open.

On a HS type, pulling out the choke cable pulls the main jet down, increasing the opening where fuel gets drawn into the air stream. It also opens the throttle butterfly to increase starting flow and rpm.

ON a HIF type, pulling out the choke cable opens a valve that allows fuel to flow through a secondary passage from the fuel bowl to the carb throat. It also opens the throttle butterfly to increase starting flow and rpm.

So, closing the "choke" on a SU means closing the extras supply of fuel and allowing the throttle butterfly to close to the idle position.

While we are at it, remember a SU does not have a traditional accelerator pump, so pumping the foot pedal does nothing.

Why would you hold the choke closed? Will just make it rich which is opposite to what you want I think.

I think you nailed it. My choke cable is trashed, even worse than when new. The choke was open part way. Since I don't drive the car in cold weather, I have put a cable tie onto the choke to hold it closed.
Thanks much!

Joe

Sounds more like flooding to me. It does not lack fuel as starter fluid makes no difference. An ignition problem (e.g bad coil or wires) would not support the sequential re-starting - one cylinder recovering at a time. A flooded engine would eventually dry out if left for a time. But if the carb is allowing fuel to flow too freely into the fuel bowl, the excess would overflow the main jet and be consumed in the cylinders... until you shut it off. A sticking or worn fuel inlet jet/needle would allow this to happen.

When it happens again, check to see if the spark plugs are wet. If so, check/clean the float bowl and the fuel inlet jet/needle.

You didn't say what type of carb you have - HS type or HIF type? How do you know it is clean? Was it recently rebuilt? It only takes a tiny bit of dirt in the inlet jet to defeat it. Or the float level might be too high. Is the choke on? - check that it fully releases.

Suspect an ignition problem. Check for spark with an old grounded spark plug when it wont start.

Lads, my 1979 998 has developed an annoying problem. While it starts right up when cold, it won’t start after I drive a couple of miles. I have to let it sit for at least one hour before it will start. It has the original carb and 123 ignition.
The coil checked out in spec, but I replaced it with a new one anyway.
The fuel pump puts out plenty of fuel.
The carb is clean.
It does not respond to starting fluid.
When I restart it, it seems to first start on one cylinder, then a second kicks in, then a third and finally the fourth. Once I’m on the road, it keeps running, though it misfires sometimes. I’m baffled. Any ideas?