1981 mitsubishi sigma won't turn off
It was a very common problem on carbureted cars, so common it was given a name: dieseling. You know, as how a diesel engine will run without spark plugs. You shut a hot engine off, there is still a little gas in the intake, and maybe the carburetor still drips a few drops down the throat. The crankshaft is still turning, so gas still gets into the hot combustion chambers, so hot it can still ignite the remaining gas, and you have "dieseling".
To rectify it, manufacturers years ago began putting an electrical solenoid in the carb's main fuel passage to stop fuel flow as soon as engine is shut off. They called this a fuel cut solenoid, fuel shut off solenoid, idle stop solenoid, or an anti-dieseling solenoid. I know datsuns had this solenoid at least as far back as the early '70's. Works very simply: turn the key on and solenoid was energized, retracting a plunger pin in the fuel passage. Turn key off and solenoid gets no power, so a spring inside the solenoid pushed the plunger back into the fuel passage. It almost entirely eliminated the problem, as long as the carburetor was adjusted correctly.
Actually, I think your '81 should or might have this fuel cut solenoid on the carburetor, and if so it may be inoperative and needs replacing. Not very expensive, and easy to replace- just screws out. Some had only a single wire connector, and some had two wires to them. It would probably be the only electrical to the carb, other than any electrical going to an electric choke, if so equipped.
Happy motoring with the old mits, Sarah. I still have an old Datsun pick-up, and now an '87 Sentra, carbureted unfortunately, lol.
Jul 27, 2013 |
Cars & Trucks