Thanks soarrich; a weak battery was the first thing that came to mind but as it turned out, the problem lay elasewhere. Guess chnaging the sensor isn't too difficult.

tim220225, thanks; guess I'll have to check it if I swap out the EI.

Funny thing was that the engine had been running fine; just suddenly wouldn't rev up normally.

Anyhow, will try a new plug first and hopefully all will be well.