After doing some research some of the symptoms of the poor running issues seemed to point to vapour locking problems
As you can see above steps were taken to add some extra heat shielding to try and combat the suspected cause of the issues. The shielding was added to the recently replaced fuel lines and additionally the electric fuel pump.
After a couple of reasonably long runs, the problem was still occurring so onto the next remedy!
After some research on the excellent HAMB forum I started to suspect the “helmet” air filter, by all accounts these are quite restrictive especially the element aspect which on some examples can at lawn mower level! So, the decision was take to revert back to the air scoop type filter that was installed when the carb and manifold were fitted. The “helmet” filter was a vanity purchase!
After one run with no air filter and a few longer runs with the scoop in facing forward mode all seems OK. So fingers crossed that the carb has now got a decent amount of air and the problem is solved.
Watch this space!