1.3 Weber Problems

So my brothers got a 1.3 Polo Coupe S but I'm sure it's the same 1.3 on Golfs.
We put a weber on and it started struggling when opening the 2nd chamber. So we removed a small restrictor that was in the pipe going from the pump to the carb and removed the return line and blasted the fuel lines to see if there was any dirt in there which didn't seem to be the case. Anyway one of these things fixed the problem but now over 350 miles of driving later if you floor it the car runs fine but if you drive with a light foot it splutters, back fires and dies. Chamber 1 kills it and Chamber 2 keeps going. Could this be over fueling? Although my 1.8 Golf never did that? 

Any help will be great!
Cheers 

Zack

Please someone with suggestions, he has work in a bit