Possible causes are
an incorrect fuel mixture, incorrect timing, corroded spark plugs, a faulty oxygen sensor, sticking float, faulty fuel injector or a malfunctioning check valve.
Not exact matches
Typically bad emissions are due to an
incorrect mixture of air and
fuel.
The result is an
incorrect air -
fuel mixture than can create a number of problems, such as hard starting, a rough idle, hesitation, misfiring or a drop in
fuel economy — issues that could, without proper diagnosis, seem to have other causes, such as
incorrect ignition timing or fouled spark plugs.
The damage is often the result of an
incorrect air /
fuel mixture,
incorrect timing, or misfiring spark plugs.
Generally, two things make power in a vehicle —
fuel and air, so if you've got black smoke you likely have an
incorrect mixture of
fuel vs air.