Have a 1991 jetta disel. just got it. smokes a lot. how do you adjust to burn cleaner. previous owner tured up fuel to get smoke. i want better mileage.

dark smoke is unburned fuel or incompleat burning ,start by looking over ignition ,air cleaner, coil , distributer cap ,rotor , plugs ,wires,

Old spark plugs were likely fouled with oil and not burning fuel (and oil) completely so minimal smoke before change out. New plugs are clean and burning everything in cylinders well including oil (therefore more smoke). If smoke from exhaust is blue, then engine oil is getting into cylinders either through worn out piston rings, or a leaking gasket. If black smoke, then this is a sign of too much fuel getting into cylinders and not all the fuel is getting burnt during combustion (a fuel system problem).

Black smoke is rich fuel (lean) have the fuel pressure regulator checked the internal rubber diafram will repture and cause the to happen

sounds like the turbo could be going bad, did you check air filter? Black smoke generally means your not getting enough air to burn fuel.

Sounds like you have a fuel-to-air ratio problem causing you to exhaust raw fuel from your exhaust pipe. you could have bad fuel injector, fuel pump, or carborator, if you don't have fuel injection system. Running that way for extended times will fill your engine with carbon deposits that will need to be cleaned up. Also could lead to excelerated piston ring wear. Be sure spark plugs are working properly to insure fuel is igniting. Since spark plugs are ignited via the distributor and ignition coil(s), this system should be check if spark plugs are having irregular ignition. Check timing to insure distributor is working properly. If you have changed gas from premium to regular, this could reduce your engine power, assuming that timing was adjusted to the previous gas. Check owner's manual for proper fuel usage.

Blue smoke is engine oil burning in the combustion chamber. White smoke would be coolant and black smoke is too much fuel. Try replacing the spark plugs to get better fuel mileage, they are most likely fouled due to oil burning.

expensive repairs are waiting for you.

Blue smoke means oil is being burned
do a compression check

no it

White smoke is a sign of unburnt diesel fuel, check your glowplugs as thats the most common cause when starting .It will start but not hot enough to burn fuel at start up, also check glowplug relay if not the plugs
Delica Owner 4m40