8f032b14_r_Visible_Exhaust___NCTCOG_org__Possible_Causes
[Engine Type] Gasoline [Visible Sign] Black or Gray Smoke [Diagnosis] Smoke may be coming from incomplete fuel combustion [Possible Causes] 
Clogged air filter Carburetor, choke, fuel injection or emission system malfunction Ignition timing off Blocked manifold Oil leaking on exhaust system
Common Causes for Smoking Vehicles or Visible Exhaust - NCTCOG.org
Possible Causes