STARTing at first try

I DRIVE a 1994 model Nissan Sentra 1,6 petrol. My problem is that every morning when I want to start the car it reacts as if it has been flooded.

I DRIVE a 1994 model Nissan Sentra 1,6 petrol. My problem is that every morning when I want to start the car it reacts as if it has been flooded.

I have done everything possible to solve this problem, including servicing the car and cleaning out the carburettor. What could be the cause?

Nadeem

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Nadeem, on a carburettor engine there are basically two things that can cause too much fuel entering the cylinders at a cold start, leading to the typical symptoms of flooding.

Hard starting, a strong smell of petrol at the exhaust when the engine is cranked, spark plugs wet with fuel, a black cloud from the exhaust when the engine does eventually start.

The first is a defective choke and the second is an abnormally high fuel level in the carburettor's float chamber.

Looking at the choke first, the choke is needed to block off the throat of the carburettor, thus creating a suction effect when the engine is cranked.

This draws additional petrol into the restricted air stream entering the cylinders, and in this way the engine receives the very "rich" fuel-air mixture necessary for a cold start.

But this idea will only work if the engine starts quickly, before prolonged cranking leads to soaked spark plugs . The shaft on which the choke flap pivots is offset to one side so that the inrushing air will tend to push the choke open when the engine fires.

Various other methods are used, depending on the carburettor, to open the choke progressively as the engine warms up. But if the choke flap is stuck in the closed position or its linkage is binding so that it cannot move, flooding will occur.

The same will happen if the ignition system (spark plugs, high-tension wires, distributor and so on) is not up to scratch, making prolonged cranking necessary.

One should always keep in mind that the problem might not lie in the carburettor at all.

The other carburettor-related problem that can cause flooding is an abnormally high fuel level in the float bowl. Many carburettors have a glass window through which you can see the float level.

The correct level is usually indicated on the window. Check that the level on your carburettor is correct before you start the engine in the morning.

If it's too high it means that the needle valve operated by the float isn't shutting off the fuel flow into the float chamber.

There are many possible reasons why this can happen: faulty adjustment of the float, a punctured float, wear on the needle valve or its seat, dirt lodged between the needle and its seat, ineffective gaskets or seals, etc.

You will have to open the carburettor again to find out what is causing it on the Sentra. A workshop manual, which explains how to adjust the float, is a great help in this regard.

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