Shift gears: your tuning notes/diary

[Jason Foster]

gotcha I was thinking the lean condition was at transition when you had the F11's  . by main circuit well you are describing the float bowl are you ?  I have my float bowls enlarged too

[Jim Ratto]

The F17 tube sure looks interesting too. Just like an F4 but even thinner... more instant fuel reserve. The F1-F5 were all designed in the early days of this style tube (and carbs that use this type, the 61450.- style that's used in IDA), in DCOE or IDM/IDA carbs, on race cars that ran on alky or fuel blend including alky. The F4, F20, F17, all have rows of holes the run well down the tube, allowing fuel to enter into bore of tube, up to static fuel level (of float bowl... that 43mm we check for from carb top). As the vacuum increases @ aux venturi, air pressure on fuel reserve in center of these tubes will "emulsify" all the way up the RPM range. The F2 won't allow this. The F11 is better suited to small cc 1600-1800 engines with mild cams, like F9.
I'm going to do more work. IDF and IDA run different because of how idle jet/progression circuits are supplied with fuel.

So far, still, the F4 runs best- even with wilder cam in my car.