I'm_a_Newbie

It all depends on the design of the carb as to how much of a problem is was/is. I don't know much about carbs on bikes.

On cars, there were generally two types, Constant Depression/Variable Venturi (Stromberg and SU are two makes of this type) or Variable Depression/Constant Venturi (Webber is the most common make of these).

The chokes worked in different ways on each type. For Variable Depression type carbs the choke only worked at low rpm to stop the engine from stalling and assist in getting the vehicle moving. Once the rpm/air flow was high enough the Choke Flap opened and the engine ran under normal fuel/air mixture.

If the SV carb is of this type then only limited damage if any would have been done.

The choke on the Constant Depression Type of Carbs is usually just a fast idle with a richer mixture which is on all the time until you turn it off, so the mixture is richer through more of the rev range. This type of carb allways seems to have a moving piston. My guess is this is the type fitted to the SV.

With the choke jammed on, the engine will have suffered a too rich a mixture. This can result in poor lubrication of the valve guides and stems and the pistons/rings. Also the valves will get sooted up as well as the rings, leading to loss of compression. Also the oil would have got thinned.

Change the oil and filter and then give it a long hard ride to burn off the soot. Shell Optimax or whatever it is called these days will help with the clean up.

Tim.