This LRO reader emailed LRO.email@example.com looking for some technical help about his Series III Lightweight's sticky carburettor.
My LPG-powered 2.25 Series III Lightweight has an SU carburettor. When the engine has reached operating temperature and I accelerate, the throttle seems to stick open. The only way I can return the engine revs back to normal is to ‘blip’ the accelerator pedal but, as soon as I press the throttle again, the same thing happens. Any ideas, please?
Craig Benton, Rainham, Essex
It sounds to me as though you need an extra return spring connected to the arm on the carburettor to pull it off positively as you release the pedal. The airflow through the carb will hold it open. The spring must be strong enough to shut the butterfly against the airflow.
This workshop advice appeared in the September 2009 issue of LRO. Back issues are available to download on digital devices here.