Something has been troubling me. The pic above shows how I have plumbed my brake master cylinder, the port marked P (closest to the push-rod) is plumbed to the rear, the port marked S plumbed to the front. So the primary circuit is the rear and the secondary the front. I plumbed the rearmost port to the rear and foremost to the front for neatness!

As the cylinder has a parallel bore, I don't think it makes much difference. However, the IVA test now assess the efficiency of the secondary brake circuit. See below..

IVA manual Section 09E
The secondary brake performance must be at least 30%,(of the
CLW or DGW as determined to be the highest) for each half of the
split system.

I don't want the IVA tester seeing P cast on the cylinder and assuming that the primary circuit is the rear!

I'm not sure if the P and S circuits share the same push-rod or if they have their own with an interposing spring. If a single push-rod is shared, it really makes no difference. Without pulling the cylinder apart, I can't tell. If anyone has taken apart their master cylinder, let me know!

Anyway, I'm going to re-plumb the brakes. This is a pain as I really dislike bleeding brakes.
For a sanity check, I had a look for pics of Caterham master cylinder installations, this is the same cylinder used in the Riot. The pic below clearly shows the P port (closest to the push-rod) plumbed to the front.


Same for the AP 13/16" cylinder.

Some good news, I have ordered an Innovate LC-1 wideband lambda sensor. More about that soon I hope.