At last I have got my 2.8 running sweet again and just wanted to share the fix as it may help others. Car was running ok but taking several starts when hot so I had tried the usual accumulator, air valve not closing,fuel valve staying open, etc and all were found to be in order. I put new injectors in as I had 2 not seating properly but after changing them it would not idle, mix adjustment did nothing so decided to check all the fuel and HT system. Did all the usual basics like valve clearances, checked plate setting in intake venturi, checked mixer screw was working, new leads and plugs, worked better but no power and still not responding to mixture screw adjustments or idle screw.
So after much reading I was fixated on the WUR have read the pirinciples of how this operated. During cold start up it reduces pressure on the main fuel feed spool to allow this to put more fuel to injectors but when the WUR is warm either due to the engine heat or the in built warm up coil, the WUR is meant to close so that the main fuel feed is harder to lift thus leaning the mixture in normal running unless extra throttle is appled in which case a vacuum causes the WUR to come into play agqin to reduce pressure on the main fuel feed spool to richen the mixture at high demand. My car was starting ok but when warm it would not idle, would rev up ok in garage but no power when on road indicating it wanted more fuel despite the mixture being set ok at idle My analysis was that the WUR was not closing fully when warm thus allowing the main fuel spool to be in a richer position than it should be so when I wss setting the mixture at idle it was based on a spool setting that was based on main fuel infeed and an input from the WUR that meant my 2.8% CO at idle was not coming from the right setting on the mixture screw, it was basically a lean mixture setting plus a compensation from the WUR still being open allowing the main infeed spool to be in a richer positoon. This is also why my mixture screw had little effect as the WUR working on a hotengine was disguising the incorrect setting of the mixture screw and not allowing it to be as sensitive as it should be.
To check the WUR I allowed the engine to cool and disconnected the WUR return from the metering head so I could see if fuel was coming back from the WUR when hot as when the WUR is hot it should be closed with no fuel going through it to the return. As I could not run the engine to get the WUR to temp I connected it directly to the battery to let the internal heater warm it up as I knew this was ok electrically as I had done the resistance check on it. After 10 minutes I put the ignition to 'on' with the fuel relay changed for the rear screen heater relay so the pump ran constantly without needing to turn the engine over, no surprises fuel was coming out of the return hose showing the WUR was still open when warm. I removed and dismantled the WUR to find a lot of corrosion in the base plate section and powered it again to find the bimetallic strip was not moving when powered despite the heating element on it getting warm. I completely striiped the unit down following a previous thread found on the forum, cleaned everything up and dismantled the bi metallic strip, put some more curvature into the thinner of the 2 strips and reassembled. Before putting the base back on the unit I applied 12v again and the strip moved about 4 mm so I resealed and repeated the test on the car to find when warm the return line no longer had fuel coming through it so the WUR is now clising when warm
Run the car up to temp, idle screw now has an effect, mixture screw is sensitive as anything and actually makes a difference to the CO which is now 2.9% and 2.7% across both sides.
Just took her out and what a dream, responsive, no flat spot, starts first turn of key, bring on the summer.
This has being doing my head in, changing the injectors for new has allowed the problem that must have always been there to show itself, I can only assume the old leaking injectors were compensating the extra fuel being thrown at them by the WUR compensation even when hot.
My main advice to anyone else who is having similar nightmares trying to fix issues and feels like they are getting nowhere is to try to get a good understanding of the system you are having problems with and then test the components individually of that system to check their functioning correctly. On this problem it came down to the basics of saying that the engine is in good condition, valves are good, electrics good so all engine needs now is fuel and air in the right mix - what can effect that then check all the parts of that system individuallly and just keep telling yourself that if you have all the components working and set correctly then the car will run so which bloody one is not working