my mk2 golf gl 1800(1987)?

well it starts fine but when it warms up and the alto choke cuts of then the engine cuts out when im driving and have pushed the cluch in to change gear mostly it dose it at junctions and i have to stop with the hand brake so i can keep the revs up but when i drive it hard it seams not to do it for a while ive made sure there is no vac leak on the carb,its doing my head in and its embarressing coz when its running good it gose like s88t of a shovle untill i have to stop at a junction can any one help in any way ....james please email me at gusto666uk@yahoo.co.uk thank you
james....