What fuel do you use? Any additives required?

for your 1974 mgb, you can use 87 octane, however you will need to add lead additives. if not you could damage your valves. if you have any other questions, about that particular car feel free to ask me. there was a time in the early eighties when I had 4 mgb gt. and one mgb.

Depends on your cylinder head, if it's been converted to unleaded (i.e. hardened valve seat inserts) there's no problem with running 95 RON (85 MON), you only need lead additive for an unconverted head. Also be wary of running alcohol rich fuels like E85 if you have viton tipped float needles, the alcohol tends to greatly reduce their lifespan.

Read the fuel additive label!