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It was my 'A' series engine that laid a real, thick, blue smoke trail, every time I deaccelerated then accelerated, until that uncle taught how to replace the very worn and broken valves!!
The problem here was that the valve stem rubber seals would become hard and would start riding up and down on the valve stem, instead of staying in the recess designed to hold them in place. On my van, I used to lay a smoke trail deliberately, by doing what you describe, if someone was sat too close behind me.
With my A40 the problem was two valves had chunks missing out of them and as a 10year old car, in those days, it was worn out! It also had a body that was not attached to the chassis as the sills and cross members, especially under the passenger seat, had rotted away, with holes in the wings. It still passed the MOT twice though!!
That car was a bargain as it cost me just £30, which I recouped when someone knocked on my door and offered me £30 for the number! 
Great days indeed! 
