Small Engines (Lawn Mowers, etc.): Tecumseh 6 hp with new carb, compression test, exhaust valve

Question
This walk-behind trimmer sat for 3 years before I acquired it.  I immediately replaced the carb.  Installed the carb, but did not yet hook up muffler and air cleaner.  It runs rough, backfires out exhaust.  Maybe the mixture is too rich?  Don't see any adjustments for mixture.  What do ya think?  

Answer
Hi John,

Some new carbs don't have any adjustments.  
Backfiring from the exhaust might indicate a leaky exhaust valve.  A low compression test would add to that suspicion or you could check the valve itself.  

Let me know what you find.
Michael