This information I'm giving is on my 2003 500cc Royal Enfield that I purchased new. I am running the `50s-Style muffler with the baffle removed. I also have a RC-2770 K&N air filter in the original filter compartment that has been modified. You simply cut off the rubber bottom of the filter to fit the original base and drill a hole in the top to run the mounting rod through. If you choose this filter make sure you type the dash between the letters and the numbers when looking or it won't come up.
I have always had problems with the Micarb sticking when giving it full throttle and have tried everything to fix it but nothing helped. It's in the spare parts box now.
I have now fitted the 30mm PWK Flat Slide Carburetor. It comes with 140 Main Jet and a 38 Pilot Jet. The description says it has a 19 Pilot Jet but that is not correct. During the 1st test run the engine would pop when I let off the throttle while in gear. Tried to adjust the air screw but it didn't seem to help. I installed the 142 Main Jet and the popping almost completely quit but I had to screw the air screw to get a good idle.
I have some larger Pilot Jets that I may try this spring when the temperatures outside warms up so I can do more testing, or I may have to move the clip on the needle. I was able to use the K&N filter and the original air filter box by using two OEM carburetor connecting tubes used with the traditional cast iron engine. One tube clamps to the air box the other to the Flat Slide Carburetor with a piece of thin wall metal tube 1 ¾ inches long and 1 5/8 outside diameter in between the two connecting tubes. . This makes for a neat & clean look.