putting the chim 500 to the test

[Ardupbegar]

Went out yesterday to put the chim 500 to the test, had a dam good drive on all types of roads it certainly lived up to its reputation. Going over the moors, it flew up, coming down the other side was ok until we were getting near to the bottom, after a mile or so of letting the engine hold me back I tried the accelerator and it started cutting out and running relay rough. it took about half a mile before it cleared itself. Any one else had that happen or know what's going on?