Volumex Backfire problem

[Morne' Joubert]

I am experiencing a backfire problem on my Volumex. When the throttle at 3000 rpm is opened quick, it backfires through the carb or and/or the boost valve on the manifold as if it is running lean. Float level has been checked and found to be okay.
The engine is reconditioned but is still standard. The valve timing is set as described for the normal 2l motor. It was suspected that the carb runs out of fuel and the fuelpump was therefor replaced with a new one. The setup with pressure valve etc. is as original.
As this is a point for point transplant into an ordinary HPE, no other experience, literature or data is available. When one drives the car has little power and it appears as if it runs out of fuel. The engine starts easily and runs smooth however due to a lack of knowledge setting of the valve timing might be wrong. The holes on the cam wheels lines up as is described in setting the valve timing in the Haynes workshop manual.

I am also in need of a Fulvia 1.6 HF cylinder head. Any help would be appreciated.