Ok just got off the phone to Errol, very helpful guy!! And he also agrees that the duration is wayy to big for just a single downdraught carby.. there needs to be more gas/air flowing into the engine to compensate for the valves being open for that period of time
But to make things sure he said to check cam timing, valve clearance and ignition timing first before branching out to anyting else, this i will do!

I will drive with this setup most likley for 3 weeks (after exams) but if any body is selling a set of dollortos or webers and manifolds please let me know....cheers
Dave