starting problem on mk 1 when engine warm

hi there every 1 im a newbe i have a 1983 mk1 golf with a 1988mk2 1.8 16v engin in im running allthe standard 16v fuel system all apart from fuel pump and pressure regulator thing not exacley sure what that bit is it starts fine from cold but when warm if left any longer than 30mins forget it it wnt start i have to crank it for at least 30-60 seconds then starts to fire just as if it were out of fuel  now this is slightly embarassing for me as i earn my living as a mechanic but i cant fix this god knows i have tryd and i built the thing from a shell help me please

Leaky injectors? A fuel pressure test will tell you if this is the case or not.

Losing fuel pressure when engine switched off. Can be a few reasons, mine was a faulty non return valve in the outlet end of the electric fuel pump next to the fuel tank (bit of debris sat on the seat of the valve), allowing the petrol to return to tank via the pump. The fuel system requires pressure to stay in the system after switching off, as the pressure prevents the fuel vapourising and thus airlocking.

many thanks guys i will give those a whirl and let u know how i got on