Rough and jerky engine performance

[khjodat]

I have a mehran 2010 model which I purchased brand new. Since last two years I have been facing engine roughness and jerking. This problem becomes normal itself and again reappear off and on. I asked some mechanics and nobody gave me a satisfactory solution. I also tuned the car engine many times but problem persisted. Recently I met another mechanic and he says that the fault lies with the fuel pump. He says that the pump has become defective and therefore it feeds fuel irregularly and when you race the engine hard for few seconds the pump develops pressure and then you car becomes smooth. Please tell me is there any logic behind this statement.

[margallar]

It is not the fuel pump, because the carburetor dpes not rely on fuel pressure.

I think your plug wires may be bad

[khjodat]

If plug wires are faulty then why the car become smooth after the engine is raced for few seconds. Weak plug wires will give persisted problem.

[khjodat]

Anymore suggestion please.

[madhouse12]

try running your car on hi octane and see if it solves the problem. if it does, its just bad quality of fuel. change the pump station then.

[racer7]

Have you checked the fuel filter and the fuel tank breather? If either of these are clogged, it will reduce the amount of fuel getting to the engine, which can often lead to poor running at low revs.

As a test, park the car outside in an area well away from any potential sparks. Switch on the engine, allowing it to idle - this presumably will cause it to stall? If so, open the fuel filler cap, and switch on the engine again. If the problem does not occur, that's your culprit! Obviously you must be VERY careful running the car with the cap removed, as petrol vapour is highly flammable.

[bango]

Its the carburetted one right?

If yes then 90% of the time this is related to the butterfly which develops a certain amount of give along its axis resulting in non-precise, and inconsistent opening every time you press throttle.

Since it is inconsistent, it doesn't happen every single time but on and off.

Remedy - get the butterfly changed/ repaired.

[khjodat]

Thanks. I have changed the fuel filter twice but problem persisted. Will check the fuel inlet cap breather. Change of petrol pumps has no effect.

[wajahat28055]

My 2009 mehran had the same problem for 6 months. Every mechanic told me a different solution. Added extra currenser, opened n washed carburettor and changed jets, changed fuel filter, did everything as jahil mechanics told me. But no use. Then one day i increased fuel from that small adjuster having spring. Now drive is smooth and better fuel average.

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[nasirjavaid]

Its the carburetted one right?

If yes then 90% of the time this is related to the butterfly which develops a certain amount of give along its axis resulting in non-precise, and inconsistent opening every time you press throttle.

Since it is inconsistent, it doesn't happen every single time but on and off.

Remedy - get the butterfly changed/ repaired.

+1

My cultus sometimes had this problem and when revved hard it becomes smooth... It was very minor butterfly movement issue... cleaned everything and now its smooth.

[tintin1]

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[khjodat]

Thanks Wajahat. Yes I think you are correct. I was also thinking on the same line. I remember that many years ago in early 2000 I took my previous old mehran car to workshop for tuning and after engine tune up the drive was rough so I took back the car to same workshop and he adjusted the air-fuel mixture screw and then the problem completely eliminated. Thanks for reminding me the forgotten clue. I will try it on my car tomorrow.

[khjodat]

As per your idea I slightly opened the air-fuel mixture screw behind carburetor and to my joy that after two years of jerky engine performance the problem is solved. Now car is running smooth and fuel consumption is great.

[wajahat28055]

I am glad u solved ur problem. Seeing these comments in 2020 lols. Just want to add a little more for readers... if the mixture settings don't work. Try borrowing from other car whole cup shaped point cover including wires, (plugs point all wires) . Then see if the problem still exists then check the wire clips which are attached to plugs are tight or loose? Tighten them with plaas. There should be no play between them. If problem persists then change plugs. If even 1 plug is short so ride will be jerky. And the most important thing is that check the distributor setting. Drive car and carry plaas with u. Move it clockwise if jerks increase, move it anticlockwise and remember a hairline difference will also matter in distributer settings.