1983 SD1 V8. Power loss when accelerating

[Mont]

I built my Gardner Douglas GD427 Cobra with a SD1 V8 in it in 1998, and it's run OK ever since. (I did a body-off refurb over COVID, new seals etc in the carbs, but mostly cosmetic). It's passed MOTs etc and all well until I drove it up to Northumberland (from Cheshire) last weekend. 100+ miles on the M6 at ~ ~70 mph / 2500 rpm with no problem. After a short stop on the A69, it restarted and ticked over OK, but pulling away it struggled to accelerate, the engine struggled but sounded different - as if not all cylinders working. It managed 50 mph, but fell to 40mph up hills. I continued, watching Temp, Oil pressure etc and all seemed normal. Eventually made it to destination, and tried to find out what the problem is. Fuel flow seems OK, checked front plugs on both sides, RHS plug whiteish, LHS plug blackish. Removed and opened up RH carb, but could find no problem. Then did the same for the LH carb -same result. Refitted everything and went for a test drive - same as before.The investigation continues - any suggestions?

[ChrisJC]

Each carb does 2 cylinders one side (outside two) and 2 on the other side (inner two). So a carb problem should follow that pattern.

Chris.