Ian, it may be a personal experience but I've always found my 1935 Speedy to be a bit ponderous in starting along with another couple of other post 1931, pre-1937 A7s with rear facing starter motors. Obviously, lacking a fixed starting handle, being pressure fed with a covered nose cone and having a high compression head may not help. Not an issue in Summer but can be in Winter but to date haven't had to resort to 12 volts. Again have kept on top of the wiring, cleaned contacts and even used an 80AH battery to little improvement and it always starts (provided battery has a good charge). Incidentally, I've found that the higher output battery has transformed starting the earlier Bacon-Slicer motors. Had a bit of spare cash and thought I'd give Powerlite a go !
Thanks James, I am a great believer in sticking with 6V and original equipment where ever possible, and I must say I have never had any issues with any of my cars, hence my curiosity, and of course I agree it's personal preference what modifications if any are carried out. I have a pressure fed speedy type engine in the Nippy and that spins into life easily in any conditions, the engine is reasonably fresh and I completely rewired the car with multiple earth returns which may assist reducing volt drop.