Cylinders 2 and 4 running lean, ideas would be appreciated

[sabbot]

I’m just starting to drive my +2 after a long period off the road and the a rebuild. At the weekend I took it on a run with some Elises. Driving 50 miles to the start of the run I noticed it was missing on light throttle openings sitting at 3500rpm on the interstate, so before I started the I richened each of the stromberg needles by half a turn. That cured the light throttle mis but when I got back from chasing Elises for 100+ miles on mountain roads I noticed that the plugs in cylinders 2 and 4 are running hotter than 1 and 2 (picture attached). I know there is some spindle wear on the front stromberg and I expected that cylinders 1 and 2 might have been slightly leaner but I have no idea why one cylinder in each pair of cylinders fed by each stromberg is lean. The vacuum for the servos is drawn from the side of number 4 inlet but the manifold is joined by cross pipes to the other cylinders (the exhaust recirculating is disconnected and the ports blanked off). Any ideas on why two cylinders can run hot / lean would be appreciated.

[h20hamelan]

Suppose if all gaps, and resistance checks on wires.
My S4, was doing the same, though with Webers. My guess has been stuck rings, from years of sitting.
So I've been doing the Italian job, with Sea Foam (some tanks I use ATF).

[Billmack]

Carburetion is the last thing to check. Do compression or leakdown. Valve clearances ,then ignition timing and all that, and lastly vacuum leaks and carb stuff