My rear carb spills petrol at a scary rate from the little vent by the fuel line, do any of you know the problem? could it be the fuel pump? i ask that cos the petrol was still pumping out for a few seconds AFTER the engine stopped running, any help guys??

Oh yeh i put my finger over the hole and the motor cut out!

i posted this in the amazon page aswell but you gusy share the same motor(well some do)
mines a '64 122s

I believe that you have a 'stuck float'. The fuel pump will pump fuel to the carbs until a float closes off a valve to stop the flow. As the carb/carbs use the fuel, the fuel level (and float level) will drop allowing the valve to open and fuel to enter the 'bowl' again. If your float is stuck, the fuel level will continue to rise and then pour out a dump/vent. If you cover the dump/vent the fuel will force its way into the engine where it will flood it out.

I am sorry that this post might be about a month and a half too late, but I hope it helps none the less.

Basically, you need to open the carb and check to see if the float is binding in its travel. Also check and see if it has become porous or has a leak. If fuel gets into the float, it won't rise to close off the valve. Either way you need to open the carb up to see what is wrong. I believe you have a SU carb of which I can't help you too much. I know how these things work, but haven't ever owned one or got my hands on one. If possible, find a rebuild kit or a set of gaskets before opening yours. If you can't find a kit or gaskets, please take care when dis-assembling to not destroy your old gaskets. Unfortunately, do to the nature of gasoline, the heat of the engine compartment, and the age of these things I believe your gaskets will break upon opening the carb up. Good luck!