Agreed on the vapour lock/evaporation theory, a few automotive engines had similar problems that were overcome by water cooling or spacing, Chrysler being one of them. This theory seems to be relevant to more than one Victa model.
Funnily though, my alternate initial theory was one of vibration and fuel leakage through this excessive vibration as it was a larger balanced rubber spacer, and was more a trial as it seems only this model around the series 3 period ran it...then it seems to have disappeared. I think if you look at the spacer it is slightly angled?
Make sure the angle points away from the handlebar,might make it a bit easier to fit?..Anyways just sharing my initial theories. But the evaporation theory seems to be the more plausible.
