Please I hope somebody can shed some light on this. Engine is fully rebuilt & has only done about 600Km. Had a basic tune-up on it just after it was fired up @ 20Km. Basic timing & sync the carbs so I could run it in. At approx 500Km I retentioned the head (42ft/lbs) & adjusted the tappets (.014" & .018"). Now that the engine had a few K's on it I could fart around a bit & try and tune it better. After quite a long session of adjusting & difficult to start problems I discovered that the middle two cylinders were not operating at idle & fast idle. On the road the engine obviously runs on 4 cyls as it had plenty of go. Then #3 cyl came good, no idea why. I removed the plugs and could see that the #2 plug was wet from fuel. Obviously no spark. I worked on the ignition for a bit & got the spark up. Time ran out on me so we left it to this week-end to finish my diagnosis.When I got the car again I did another power drop test and now it was back to the two middle cyls not working again. I performed a compression test #1 195, #2 195, #3 180, #4 195. I then performed a leakage test. #3 cylis leaking into the crankcase. I was looking for a blown head gasket but with 60PSI, I can't hear any air leaking into the adjacent cylinder. This compression variation however is not the problem. So it was back to the drawing board. I checked the distributor cam & found it to be bent quite substantially and the top bush was warn. Points were only just opening on #2cyl. I recond another distributor but this did not improve the 2 cyls that were not working at idle. Initial timing is set at 5deg BTDC.Removing the HT leads one at a time shows #2 & 3 cylinders are dead. Plenty of spark is available and no difference is heard when the spark is made to jump across to the spark plug. Both HT leads can be removed at the same time with only a small drop in fast idle and the exhaust note goes quiet. When both leads are off & one is put back on, either one doesn't matter a difference is noticed but only slightly and the exhaust note comes back. If#2 lead is left off & the engine is revved, a miss can definitely be noticed and the same for #3, this tells me that under revs/load the cyls are working. I have elimated brake booster leak, PCV problem. Checked the intake for vacuum leaks with an ultra-sonic stethoscope(no leaks except at the throttle shaft of one carb, checked this by dropping petrol onto intake manifold (no difference to idle) dropped petrol on throttle shaft & engine died from overfuelling, replaced the cracked distributor rotor and checked all HT leads &cap.The carbs are still running slightly rich and I have the jets up almost flush. The floats are correct. Attached are the plugs to read. Black on outer edge backs up the slight over richness, the centre porcelain is still pure white. These plugs have only done about 40Km. All indications point to a failure of head gasket? Two cyls next to each other that do not share the same carb. The inlet ports are Siamese andt herefore a carb problem is unlikely as one carb feeds #1&2 and the other feeds #3&4. I hope I have put enough info in here for the gurus. Hopefully someone has come across this before. Car has RE13 cam but is otherwise pretty standard only twin 1/1/4 SU. Using BP Ultimate fuel. Basically the car is running on 2 cylinders at idle but 4 cylinders under load.
Any ideas?

I don't know why they do it really, but I find with long duration cams and big valve lifts this phenomenon is common. I suspect it is charge robbing between inner and outer cylinders due to the siamesed inlet ports.
My 1360 (RE282 cam & 1.5 rockers) does this too, no misfire, no oiling of plugs, it'll idle all day without fouling them up, they are all light tan colour.

With 86.6HP at the wheels I don't think I have any mechanical problem.. it's just the way these things work.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks DR for your response,I will now be able to sleep at night as these 2 cylinders were driving me crazy. I am using BP5ES they are all a white porcelain colour or should I use BP6ES's.

BP5ES are fine in city running, but too hot for prolonged hard driving.
I prefer BP6ES for mine (but I use Bosch W7DC, the equivalent).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.