Exhaust "popping" on overrun?

[Ian Williams]

A genuine Lucas DK4 bush is made of a porous oilite material, and so should not need a drilling, however many get replaced by solid brass with no lubrication hole and quickly fail. Accuspark seem to have attempted to overcome this by fitting the top bush so far down the body it is actually below the oil hole, they have also made the bush from steel, I suppose the thinking is to reduce wear??But then they thoughtfully compensated for the lack of wear by providing extra clearance in the bush!!!