Bought our daughter a good 2nd hand run around car, a mitsi mirage f, 4G13 good clean car... however...

We have noticed that...when starting first thing in the mornings the car would have no guts at all and would chug along until it warmed up. This is not to say we start cold and race off..but as you normally would.

I pulled the plugs and found them to be a dry sooty condition. Not knowing alot about this car, obviously running rich as indicated via the plugs, we took it to a mechanic,,claimed the carb was ok, he tweaked it abit, new plugs..daughter was away for the weekend with the car, and on her return I pulled a plug, only to find the same condition, dry soot.

What Im really looking for is any ideas on the possible cause to this? Could it simply be the oxygen sensor not working correctly? Or is it a long line of possibles.. the mechanic we took the car to said to change the cam belt. Ok the belt is due, and I have one in the shed and will replace it next free weekend I get..but I fail to see how replacing the belt would help the fuel mixture? Or am I thinking along the wrong lines?

I hope Ive made some sense.. and would be keen to get some ideas.. thanks alot.

From what you wrote it seems that the car is not running on fuel injection, therefore it cannot have an oxygen sensor. The carburetor on the car, should be the first thing to suspect. Check whether the choke is working. This needs to be done when engine is cold. The car should idle at a higher rpm and when the engine gets hot it should lower to the normal idling rpm. The choke mechanism is not that straight forward on the this carburetor as it does not use an additional butterfly as the conventional carburetor. So the previous test should be the easiest to check for choke cold start functionality.

When you said that the plug was dry sooty condition does this means that its powderish black. If this is the case the car is running rich on fuel. If the plugs are black oily and with a lot of carbon deposits this means that your valve guides are leaking. Did you notice and reduction on the engine oil level. If this is the case you can still get by, but need to top up engine oil level moderately but you can't tune the carb by inspecting the plugs. When the car is running an ideal mixture the color on the plug electrodes should be light brown. Lean and it will be whitish. The idle screw mixture is on the back of the carburetor tighten to rich and loosen to lean. let the car warm up firs before you do this. And check the muffler end if the gas is moist you can feel water on your hands that means that your idle mixture is ok.