Data!

Managed to get some data off the new AFR gauge and attempted to make some sense of it. For reference our engine baseline setup was as follows:

12 degrees initial advance

34 degrees all in at 3000rpm

Carb calibration point 10 

.116 primary jets

.073 x .047 primary rods

stock secondary setup (.017 rods)

The first bit of data I got had showed that at cruise it was giving roughly 12.3:1 AFR which seemed a bit rich. On WOT it was bobbling around 13 ish which seems ok and is normal. Based on no real knowledge at all I decided to go back to the stock calibration (position 1 above). Unfortunately in my carb calibration kit I didn't have the correct combination of rods and jets so I ended up going to position 9 instead which has the following setup:

.113 jets

.068 x .047 rods

This should lean things off a tad on partial throttle acceleration and may help the cruise mixture (hopefully)

We went on a good blast to the local club meet just north of Ely and gathered plenty of data at all sorts of engine conditions. Frustratingly we lost the revs logging after a few minutes so we don't have any RPM data.

The screenshot below shows very clearly what is going on for a good hard bit of acceleration. The manifold vacuum (red) goes to zero when you push your foot to the floor, then you can see when I changed gear as the vacuum rises momentarily. The blue trace is the air fuel ratio on a scale from rich (bottom) to lean (top). 

First off its pretty obvious when I floor the throttle there is a lean spike. This would suggest the accelerator pump shot isn't enough. On full throttle as the revs rise the AFR stays relatively constant at about 14:1. This is too lean for best power. It needs to be somewhere around 12.5:1. This would suggest I'm too lean in power mode. It seems to show that my guess as to the improving things by going to calibration point 9 was a perhaps a bit misguided so I returned to cal point 10 (are you still following?!). I also moved the accelerator pump shot to the hole closest to the carb to give a bigger pump shot.

I realise that the slightly lean WOT mixture may well be the secondary jets but I want to tinker with the primaries first to make sure I properly understand what is going on.

One useful thing from the data is that on very light throttle cruise the manifold vacuum is about 9.7in.hg. This will be useful when I come to look at the staging springs. Chatting to the chaps on the forum its entirely possible that the springs are too strong so the rods are in the "up" (rich) position at cruise because the vacuum isn't sufficient to keep the rod down in the lean (cruise) position.

Went out for another drive to collect some more data with the new setup.

First thing I noticed is that the lean spike hasn't gone away. When driving the car it seemed to bog a bit when going for mega throttle so I think I might put the accel pump shot back to the middle slot as the car felt better before. 

The good news is that on WOT after the initial spike, the mixture is closer to 13:1 - an improvement from 14:1 but still not in the optimum zone for best power.