Many thanks for your replies. Very much appreciated. Below I have compiled some more information:
- Some time ago I installed a relay in order to provide a liable 12 Volt connection for the choke, fuel pump and ignition coil/with ballast (all connected to this one relay output). I took the 12 Volt from the starter relay. It provides full battery voltage with all consumers connected. It did when I installed it. Maybe I should crosscheck.
- The misfiring sounds like a rev limiter. It is not firing into the carburetor
- Misfiring does not occur when revving the engine up with primary throttle only. Only at full or almost full throttle position (primary and secondary open)
- I never tried revving the engine up with car sitting still (want to keep a good relation with the neighbors)
- The dizzy is new (MSD). There is no rev limiter as far as I know (I have the standard Ford ignition box, green)
- At this point I would exclude valve floating since it does not occur with primary throttle
- When misfiring occurs, I get scarred and immediately remove the foot from the gas pedal. Do not know whether it is a wall or whether engine would rev up higher.
- Engine is not surging
- Misfiring goes away when lifting-off the accelerator pedal
- I did not check the suction line for the fuel feed yet and do not know whether the suction line was modified by the previous owner
Many thanks for your support
SIG