When I was a car mad teenager I used to use this stuff in my JPS Capri and was well impressed when a load of black dirty looking smoke came out of the exhaust, I thought it must be cleaning out a load of crap from the carb and valves, but of course mainly the smoke was just from the oily rubbish I had just poured into the spark plug holes and carb! More recently I have used the injector cleaner, and have to say I didnt notice a blind bit of difference afterwards. I think that modern petrols are a lot 'cleaner' than older fuels, and contain detergents themselves anyway, so I would think that these products are now a waste of money.