Fuel issue

[Surly_Z]

I had issues with my L28's carbies and fuel, where I'd get a misfire and a really awful clang sound during high revs.

Just had a brand new SUs installed and tuned, car was running smooth, good fuel economy, no smoke.

 

However, all has changed and the problem has come back. I am now running on 3 cyclinder most of the time as it looks like the second carbie (closest to firewall) is not getting enough fuel.

- My mechanic said it is dirt in the fuel lines, so I've put 2 new filters between fuel rail and carbie (a total of 3 fuel filters now!)

- I've also pulled apart dizzy and everything is clean and working.

- Brand new spark plugs and leads

 

Could it be the fuel pump? It's the mechanical pump which looks pretty old. With fuel filters attached just before each carbie I can see that one is receiving more fuel than the other, should this be the case?