Qaisar all the questions that you have asked are very pertinent and I am glad that you asked them.
Before I reply your questions I want you and other interested readers to view my web site where under “About us” tab I have given an animated diagram which explains how an injector works. So grab the link by clicking my id on the left of this post and selecting visit umar2606’s home page
Now coming back to your questions…
- if petrol flow is less due to sediments then why unburnt fuel from exhasut ???
I am sure you know that fuel injectors are electrical solenoids. The injector contains a pintle (valve) that closes off an orifice at the nozzle end as you have just seen in the diagram. When electric current is supplied to the injector, the armature and plunger move a short distance against a spring, allowing fuel to flow out the orifice. Because the fuel is under high pressure, a fine spray is developed in the shape of a cone. The spraying action atomizes the fuel, adding it to the air entering the combustion chamber. Now as you know that atomization of fuel and the spray pattern are two very important phenomenon of electronic fuel injection system.
In some instances, deposits on the tips of the injectors can change the desired fuel spray pattern and affect the atomization, resultantly the fuel does not get atomized properly and takes longer to evaporate in the cylinder. This is how we get smell of unburnt fuel in the exhaust. Let’s summarize this whole phenomenon in few words. When the injectors are not clean they do not atomize or vaporize the fuel efficiently. Badly vaporized fuel takes longer to evaporate in the cylinder. In every next cycle more foully vaporized fuel enter the cylinder and generally cause drivability issues as well as bad emissions.
Your second question is easier to answer 
- what is the relation b/w sedimented injectors and engine wear ????
As all of us know, that the crank shaft receive power from the cylinders through connecting rods which on their other ends are tied to the pistons. Pistons move due to the combustion and deliver the power to the crank shaft which is further conveyed to gear and the vehicle moves. Imagine a crankshaft which is receiving equal power from all the cylinders to which it is attached. Such shaft will move in a harmony and will perform on a synchronized optimum level. Now imagine another crankshaft which is receiving altogether different jolts from each cylinder it is attached to. Imagine cylinder 1 is pushing the piston with 5000 psi cylinder 2 with 3700 psi cylinder 3 again with 4700 psi and damn… the 4th is just producing 3150 psi….ouch…what a dissonance…Every one can imagine how such an engine will depreciate. This is what happens when the fuel injectors are not firing the symmetric amount of fuel. And symmetry is for sure disturbed when the injectors are clogged
Your third question was
- if we are injecting less fuel (due to sediments) then why fuel average goes up ????
But I am afraid I wont be able to answer it in detail. There are two reasons for a brief answer… 1 because I am quite convince that you are an intelligent guy who can understand the whole story from one sentence 2 if I went in detail the power will cut off and the load shedding will restrict me of posting my reply :o
The answer to your question is that when the injectors are clogged you don’t get desired response from the engine as its already leaning due to fuel starvation. To rev up, you push more on the accelerator and inject more fuel into your engine which go waste yet you don’t get enough power.
