Spent 2 hours with freshly acquired tools, pls an assortment of old ones making progress with Otto. Unfortunately that did include jetwashing my arm and sleeve with coolant while draining the system now I have a 21mm socket for the radiator drain plug.
In the end gave up at this point.
I think the top end overhaul is going to be very useful. There was quite a bit of sooty gunky oily mess in the plenum / ram pipe section, but I think this is our real culprit for the issues.
I'm sure I haven't seen thick carbon soot like that on an intake before. Suggests to me that whatever is wrong we have been getting combustion with number 4 inlet open, and that will be the source of the gasket issue / valve stick to number 2 too. If the gasket has blown between them and 4 is burned or held off the seat then it would be a tad problematical.
Further delving will be complicated by inability to remove the exhaust heat shield bolts - currently thinking best option is to separate at downpipes and take manifolds off with the heads for better access. Please tell me that is possible and they clear the chassis legs, plumbing of various kinds / fluids, wiring, etc?
Also recommendations on slim 5/16 to get to the lower / outer rocker cover bolts. My 5/16 is too bulky to get in there, although it fitted the inner / upper ones fine.
And what am I missing with the injector / etc wiring plugs? Everything else I have worked on has had a wire bar section that pushes in to release the plug, or a single / double plastic press in catches. Those look like the wire bar ones, but with the bar missing, and I don't want to screw them up trying to get them off. Enough problems already....