Sputtering and immediate power loss

We are having issues again with running. The car is becoming increasingly difficult to start. Once started it runs ok and then drops rev as if everything has cut out for a milisecond. generally when you are doing a steady speed on harsh acceleration it is good but when you are holding it constant it drops.

Within past year, New Coil, new filler neck, new points, new condensor.

Within past week New rotor arm, New dizzy, New HT leads

Checked fuel filter no debris, checked fuel tank filter no bits tank has been flushed about a year ago when filler neck was replaced. We have put carb cleaner into carb today and this has not helped.

Still running a pierburg 1b3 could this be the issue? There is a smell of petrol sometimes when you stop however I have checked the hoses and joints.

I am going to check the air filter which is a K+N and has been cleaned once in the past year.    

Any suggestion welcome.

Also can I uprgrade to a weber 32/34 with the correct mounting gear? This may be an option.

I think Tesco may have the answer going to speak to them