RE: Old Webra 32
Dr.,
You may be right, but I can only judge by my own experience in my own country's weather.
I had one Webra (a .40 Speed) and ran it on 5%.
Starting backward is usually caused by over-priming... but also by detonation... so you may actually be experiencing an effect of high nitro.
I do suggest that you try running those Webras that you own, on 5% nitro.
You may be surprised by the performance (or by the lack of difference from your old fuel) and by the much lower fuel consumption.