I have a small gas leak " some where " but mechanic said he can not do a smoke test on it , what reason would there be to not be able to run a smoke test ?
We need clarification on your terminology. Do you have a gas as in gasoline leak? That would mean you have a fuel leak. Fuel is liquid and can not be smoked. Or do you mean an EVAP leak which is vapors. EVAP systems can be smoke tested.