My Dad drove a lot of miles in bubbles, he owned a KR200 which he toured France in with Peter Green. Only issue was a broken carburettor spring, which was fixed with a large washer.
The following year they drove to Gibraltar in Peter's Heinkel. This turned out be a bit of a stretch, they covered the 3500 mile round trip in a fortnight. My Dad says they never seemed to stop driving which I think frayed tempers at times. No mechanical problems apart from a bent trackrod which wore a tyre out and battery acid burning holes through their tent when Peter turned it over into a ditch in Spain, almost decapitating my Dad in the process who was shooting cine film at the time out of the sunroof !
The cruising speed was always kept at about 40mph, and that sounds about right, especially where four strokes are concerned. Two strokes can handle more abuse I think, being very simple engine designs. Vic Locke and Brian Westoby, both Isetta high milers in their day said the same thing- 40mph, with maybe the occasional burst to 45mph.
My Mini 1000's were always happy at motorway speeds, especially if they have 3.1:1 final drive ratio as fitted to post '84 cars. A stage 1 kit is a cost effective investment and really opens up the engine and lets it breath. Mine certainly never fell apart- you must have been driving some pretty clapped out mini's if that was your experience. My main gripe was the quality of the seals on brakes and pot joints- always going home, and I bought the best available, not cheap pattern parts.
