I've had my 8N for 2 years and it has ran great . . .except for a very slight, barely noticeable miss at idle. I decided to tackle this problem earlier this week and performed the following: replaced the points, condenser, plug, plug wires (these were due for replacement anyway), replaced the distributor bushing, and R & R'd the carb (completely disassembled, soaked, blasted, soaked again, and blown out).
The tractor runs just as good as it did before all of this work . . . and still has the slight miss. I also noticed that it idles best with the idle mixture screw all the way in. As much as a 1/4 turn out will result in a rough idle. If I remember correctly, turning the screw in will RICHEN the mixture. If that is correct, then I am lead to believe there could be a vacuum leak that the extra-rich idle mixture is compensating for. If that's the case, then I have to believe the manifold could be the issue.
Am I on the right track here?