Deffo 2 hours work on a rear disc model, probably more, so 100 quid isn't too much.
Should only take an hour or a little more maybe on a drum brake model.
This simply because the drums can come straight off, disc brakes need to be totally dismantled.
Dan,
It sounds like your fuel mixture is TOO RICH, cos you have high level of hydrocarbons due to unburnt fuel.
You can do this yourself with a gunston colortune from Halfords.
Plug it in instead of a spark plug, connect the test spark plug to a ht lead, then observe the colour.
Adjust the co screw until you get a blue flame with orange tints in it.
It works well in the dark
