If you can smell it with your nose, it mean they will not pass emission.

I understand the gases they test for as colorless and odorless. But if one can smell it, there is no way it would pass.

Is this statement generally true?

 

Well, if you can smell it your HC emissions will probably be too high. Just run the crap out of it beforehand to get it nice and hot. If your timing is advanced, retard it a little. Lower the fuel pressure if you have an adjustable regulator (life saver). Use a good catalytic converter for the test (no gutted or high-flow cats). Just watch out if you reconfigure your timing and fuel pressure, because it might be running too lean and that could lead to detonation depending on your compression and fuel octane.

Retarding the timing a bit can help out a little to be safe, but you'd need to play with it. Use the lowest octane fuel that you can safely use with your engine's compression ratio, because higher octane fuel will take longer to burn and may leave incomplete combustion (higher HC reading). This will also lend more to detonating when using a lower-octane fuel, so just be easy if your compression is too high. All depends on your setup