Small Engines (Lawn Mowers, etc.): Engine surge/backfire on Honda GC160, honda gc160, air mixture

Question
I have a husqvarna tiller model# 917.296250. The engine is a Honda GC160. The engine seems to run ok at idle and partial throttle. At full throttle it seems to surge and under a load it will backfire. I have disassembled the carb and cleaned. It seems to do a little better but still surges. If I hold the control arm for the throttle valve steady it runs perfect at all RPM ranges. Is it possible I am missing a spring for the carb throttle control to hold it steady?  Or do i have an internal engine problem?

Answer
 Hello Kyle:

 If the Carburetor has the Air Mixture Screws, then the Main Jet Mixture is Too Lean. If the Carburetor is a Factory Set Mixture Type, then the Carburetor Needs Another Overnight Soaking. If the Gas/Air Mixture is too Lean the Engine will Backgire After a Certain RPM is Reached. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John