I may be getting confused here but I sent somebody my 'Eddy' spreadsheet which allows you to compare any jet and rod combo with any other, I thought that it was you, maybe not.southernd wrote:So say 67/56 is leaner tab 62/52?
Anyway, it is not quite as simple as just looking at the rods on their own, you need to look at the jets as well. The numbers on the rods are just thou of an inch diameters, so a 67-55 rod has two diameters the cruise is 67 thou thick, the power circuit is 55 thou thick. (You get the idea for other rods 65-52 etc. By the way there isn't a rod that is "67-56")
The numbers on the jets are just diameters, a 386 jet is a "3" series jet that is 86 thou in diameter. A 413 jet is a "4" series jet, in other words a jet that is over 100 thou in diameter, a 413 jet is in fact 113 thou in diameter. a 410 jet is 110 thou in diameter, a 407 jet is..oh you get the idea.
The fuel flow though the primary side of the carb is determined by the size of the primary jets BUT remember that the rods are poking into the jets which makes the flow area smaller. When the rod is in the down (cruise) position it blocks off more of the jet than when the thin part of the rod is in the jet.
So when looking at a set of rods that are smaller than the set you have currently fitted to the carb just changing the rods will make a big percentage change to the setup, it will be a lot richer but if you fit a smaller jet at the same time as changing the rods then even though you have fitted thinner rods the setup could in fact be a leaner setup.