Capt,
Couple of things to consider before you clean your carb and put a new carb kit in.
- Make sure the vent cap is open on gas tank. Closed will make it difficult for the pump to pull fuel at higher speeds. Also make sure the vent cap opening is not clogged with dirt or old oil,etc etc.
- Look at your fuel lines and connectors from the tank to the motor, from the connector to the fuel pump and from the fuel pump to the carb. Check for cracking, looseness, and leaking. Possibly with cracks or loose connections air could be entering the system and displacing fuel.
- With a spark checker, check both cylinders for spark at least 1/4 to 5/16 inch of gap. Should be a good snappy blue spark.
- Make sure the fuel you have in your tank is fresh, phase separation can happen with ethanol enriched fuels and water accumulation.
These are just a few thoughts before you dig in your carburetor. If all the above is ok, then you may have clean and place a new carburetor kit in your motor. From the sound of your symptoms, your high speed jet may be gummed up or float needle maybe gummed up and sticking. The reasons for suspicions, is that you can start up your motor fine and idle fine.
Someone, brought up an interesting point a month or so back, when they where having similar issues, but they were having rough idling as well. The issue was fuel vapor lock. The fuel that they were using was a winter blend and the fuel vaporized in the fuels lines and fuel pump at lower temperatures with record high temps. So, try fresh fuel/oil mix and see if your problem improves.
Hope this helps you out.