Boggy,
The breather hoses that go from the top of the oil tank just in back of your engine cylinder to the catch can under the seat and from the catch can to the back of the timing chest (the big bump just in front of where you add engine oil). These two hoses and the catch can need to be cleaned every once in awhile, especially in cold damp weather. The hose that goes from the oil tank to the catch can is the worst offender.
I use the gasket and the "O" ring. Without the "O" ring mine will suck air and run just terrible. Use grease only on the "O" ring to keep it in place, in the grove, when installing the carburetor to the cylinder head.
If these don't work to make your bike run better, maybe it's time for your Royal Enfield motorcycle shop to take a look. It's good to support your local motorcycle shop.
Royal Enfield motorcycle shop people are good people. The good people at Vince's Motorcycle Store in Lacey, Washington work on my motorcycle.
Cheers,
Bill