As soon as I got home from the national I whipped them out, 451 mile round trip, averaged about 35mpg, there were a lot of hills in the area and I had a full load. What do you think? Also why do plugs 1&4 have a red tinge in places?
These look fine - slightly on the weak side for power but probably perfect for economy. The red tinge...are you adding any silly chemicals to the petrol???
NGK BP6ES is what they are, done about 4/5000 miles. The Champion set that they replaced had much more rounded electrodes, the ground electrode was rather thin also.
Plug condition looks good to me but the gaps look a bit wide!
Should be set to 25 thou or a little wider if a high performance sports coil is fitted.
I would agree with BMC in that the red tint could be caused by fuel additive.
Because of the Siamese porting and design of manifold on the Morris 5 port head No1 & No4 flow slightly differently to No2 & No3 and can cause a slight difference in the combustion process which may result in spark plugs having different characteristics when removed as exemplified by your photos even if the engine is working efficiently.
35 miles to the gallon is good going if you were fully laden and had hilly terrain to cross.
