Messing around with my car

Wow I'm calling it MY car now, but for the sake of correct grammar and keeping it short and simple, yes, MY car.

A 1981 Datsun (the name before Nissan) Sunny 120Y. The Sunny was then succeeded by the Sentra and Latio.

 

Post not suitable for those who know nothing about cars and I shall not be responsible for any splitting headaches due to the vocabulary used.

 

So the story was that one night picking up my brother from Bangsar LRT, on the way back the engine was extremely rough and weak with the aircond and headlights on. The engine even stalled twice at traffic lights. After consulting dad, the loving and all-knowing owner of this fellow for about 10 years plus, he suggested I increased the ratio of air and petrol going into the engine (aka making it rich) as well as it's idle RPM. I did this by adjusting two screws at the side of the carburettor:

The two being the one at the left and right sides. The one in the middle is just to hold the carb' in place.

So after adjusting these two, the engine was very stable and smooth with all accessories turned on. All was well until I saw my fuel efficiency plummet like a stone. Originally I was doing about 12-13km/liter for mostly town driving. This is comparable to a Saga or Myvi. After I tinkered around it has dropped to about 9km/liter. So naturally the solution is to bring both the air/fuel ratio and idle RPM back down again. So I went back to the screws and did more turning.

This afternoon when heading out to Taipan for lunch, the engine would stall whenever I came to a stop, but would start up again and idle just fine. Under the sun, wearing of all colours a BLACK shirt (damn smart right me), I did more screw turning to try and fix it but to no avail.

The heat got the better of me and I retreated back to headquarters the internet to look for the solution while I waited for dad's reply. click click click, tap tap tap, and sure enough one of the (common!) causes was setting the air-fuel mixture too lean (too little petrol), and then setting the idle RPM screw too high to compensate.

So at 5.40pm, with the sun being a bit more merciful, I went back out and screwed (pardon he pun) around a bit more, and finally, success! Well, sort of. The stalling engine was no more, but then came traces of black smoke from the exhaust and split-second flatspotting (temporary lack of fuel mixing with the air) when I press the accelerator pedal lightly. 

 

When dad finally called, he confirmed my suspicion that human error was the cause of the stalling. 

The black smoke he says is PROBABLY because the choke plate is stuck closed. You know how you choke somebody and deprive him of air? Yeah the choke plate does exactly that. It's purpose is to make easier cold-weather starts. He says best leave it alone, and shouldnt be concerned about it. Good thing I'm not much of an environmentalist.

The flatspotting also, shouldnt be much to worry about.

So now all that remains is to top up the tank and monitor my fuel consumption. Hopefully it improves after this...