Here is the History: Working on a 1966 N15 with 389 monobloc carbs. One carb is chopped model. I am having trouble getting one cylinder to idle. I am pretty sure its the idle circuit because the bike runs well when throttle is opened, but will not fire on one side on idle. This all started because I had to swap out the chopped carb because the original was warped and the slide was sticking. Now the replacement chopped carb wont idle. I have flushed and probed all the idle airways that I could find. Still wont Idle. I then compared the 389 chopped carbs. The only difference between my 2 carbs is that the original carb had a hole (port) drilled from under the carb side cover through the inner wall into the area were the main jet would seat. This would in essence form a gas reservoir. On the replacement carb (the one that wont idle), this hole is not there and therefor there is no gas reservoir forming. My question: Is this hole necessary? And could this be why the idle circuit is not working properly?