Blown head gasket

I just completed doing a head gasket repair on this car because of internal leak. I did the same thing two years ago and was successful. But this time I am puzzled. I am not sure what is wrong. The car stalls after running for less than a minute. I have checked vacuum leak. Put new spark plugs. Replaced the idle speed valve or control valve. When I start seems like sounds like air leak. I also notice like exhaust smoke around the engine. I have checked both exhaust manifold and the gasket and I cannot see a leak. When I push the gas it stays running but as soon as I release the gas it stalls. Can you help? Could this be a piston problem? What else would emit exhaust fumes around engine? I have not checked compression.