Small Engines (Lawn Mowers, etc.): Blower and Trimmer flooding at full throttle, adjustment screw, carb settings

Question
Hi John,  I have a Honda trimmer and Blower, both quite new (under 20 hours) and both GX-25 motors.  On occaisions both refuse to rev to full throttle.  After a several seconds at max RPM they  lose revs.  Holding the throttle open will cause both to die.  

Feels like they're flooding.

We live in a remote area of north OZ, very hot and humid, but no altitude issues to consider.  At first I thought my fuel might be losing octane in my (very hot) garage, and I haven't completely ruled that out, but the supplier said NOT to use premium (higher octane) unleaded in them.

Today is cool, only about 30 celcius, but 90% humidity and my blower needs constant throttle adjustment to keep it running.  3/4 throttle will run fine, but wide open causes it to lose revs after a 5-6 seconds.
My Honda GRU-165 mower has never had the same problem running on the fuel from the same can.
Wondering what my test method should be. Should I up-spec my fuel? I'm wary about adjusting my carb settings from the factory settings, but quite capable of counting quarter turns if think that might be an option.
let em know if you need any further detail.
BRAD

Answer
Hello Brad:

>>It is Possible that the (H) Carburetor Mixture Screw Requires a Slight Adjustment.
>>Try Turning the H Adjustment 1/4 Turn in to Decrease the Fuel At Max RPM's. I Don't Suggest Going Over 1/2 Turn in.
>>If this Does Not Correct the Problem, then Return the H Adjustment Screw Back to the Original Setting and then Turn it Out 1/4 Turn. **Remember to Operate the Engine After Each 1/4 Adjustment.**
>>I Suggest you Check the Exhaust Port and Muffler before Any Adjustments are Performed.
>>The Following is a Basic Instruction File for Doing a Diagnostic on the Engine for this Problem. Any Input is Appreciated. **Remove the Muffler and Make Sure the Exhaust Port is Clear. If it is, then Try to Start the engine with the Muffler Off. If it Starts and Runs Properly, then Clean the Spark Arrestor Screen in the Muffler or Replace the Muffler if Required.
>>If the Exhaust Port and Muffler are Clear and Adjusting the Carburetor Screw did Not Correct the Problem, then there May be Water from Condensation (Very Hot Garage and Gas, even in Plastic Gas Containers will have Condensation inside the Cans) is Restricting the Gas Flow at High RPM's. This Symptom can Sometimes be Mistaken for the Engine Flooding at High RPM's, when the Engine is Actually being Starved for Fuel at High RPM's.
>>You will want to Remove the Carburetor and Blow it Out with Compressed Air. If you are Carful, you can Reuse the Gaskets and Diaphragms and a New Kit is Not Required.
>>If you can Make a Place that is Cool and Dry to Store the Gas; this would be Highly Recommended.
>>Please, Do Not Hesitate, If you Hit a Snag, if I Missed Something or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

>>PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John