Hi, I have a slight problem with the left carb on my 1981 CM400 Custom. After a complete rebuild on both carbs, I started it, and warmed it up. At first the left cylinder wasn´t getting any fuel, so I put my hand over the LH carb to try and clear it up. Now, I was getting ignition on both cylinders, so I revved it up to about 4,000RPM. I tried to rev it up to 5,000, but it stopped revving at 4,100. It didn´t die, it just kind of bogged down, even with no load. I also idled it down to 1,200, like the manual says, and tried to get it back up to 4,100. When I gave it throttle, it bogged down for a second, then revved up until it hit that same point at 4,100 where it wouldn´t go higher. I´m thinking it is the air cut-off valve. Any ideas?