You may want to check some of these things:
1- Check your Battery (under a load tester)
2- See if your Carbs are Vented with the 10" Rear, 11" Front hoses and not the Running together in the Y configuration.
3- See if your Fuel is not Boiling -insulated Tanks
-Have you done the Flapendectomy?
- Also Run a Fuel Treatment -like SeaFoam