16 hp v twin briggs and stratton engine very hard to start when cold.
New plugs fuel and air filter still same problem.
Exhaust smells very sulfur like and burning sensation in my nasal area.
Could this be a air fuel mixture problem or blown head gasket?
Normal smoke from exhaust but will sometimes backfire when trying to start.
Used daily approx 2500 hrs.
Don't want to mess with carb adjustment until I know this my be the problem.
Thanks for any help.

If you are experiencing a burning in your nose, it very well could be the mixture. Adjust and try and "clean up" the exhaust.