Moving my facet fuel pump from the splash guard to near the tank as its too high above the tank and is taking time to pick up when in lower gears (assume getting air in the system) so hopefully moving the pump much lower will solve the problem, and the splash guard is being replaced so didn't want to drill additional holes in it. Planning to put the pump on the back of the seat box just above the tank and need to cut into the existing pipes but there is a threaded connection to the pick up pipe with a what seems like plastic hose of fairly narrow diameter (maybe 7 or 8mm) which the disappears along the chassis under the floor where I can't see it but comes out in the engine bay as a copper hose which then joins a 6mm rubber hose so I assume its 6mm internal dia? Other issue is the feed is 6mm and output on the pump is 8mm but I can get adapters to cover that. So can i cut the existing feed near the tank, attach to the fuel pump and get an adaptor to join the 8mm output hose to the existing and then connect up at the carb end? Its a P6B V8 just in case the sizing at the carb end seems odd.
FFG

I think your about right at about 6mm or 1/4 bore, mines a diesel and the OD of the plastic pipe is 8mm.

I would have thought that if you have a fuel starvation issue or air getting into the system it would be more noticeable in the higher gears.

Thanks. The Facet fuel pump is supposed to be 12 inches max above the bottom of the tank - its about 3 foot now so may be the issue.

Have a look at this site and renew all your fuel tubing should not be necesary to keep changing sizes.
https://www.ssldieselparts.co.uk/index.php