misfire when hot

Make sure the distributer and coil are well grounded.

 

will also check that.

 

[ but are you implying a carb issue? /U]

Yes, & several times so far in this thread of yours.

You are describing a lean condition when on the secondary fuel circuit.
It doesn't sound like you are describing a faulty ignition because you say it does run good at all times except at operating temp under throttle and load.

The primary fuel circuit sounds like its fine.
The accelerator pump is working, but that only handles the transition between primary and secondary and that transition period only lasts only a brief moment.

One piece of debris getting dislodged then relocating itself to a new location in the fuel circuit can cause a sudded onset of your symptoms.

 

1st thing that comes to mind from cold to hot. Your rich when cold. So lean misfire.

 

I thought it was a carb issue too but it is always nice to have smarter people than me to come to the same conclusion. It is of course also very useful to hear every bodies thoughts and thinking. I know it is hard to diagnose an engine misfire over the internet.
I will report back when I have had chance to perform the vac tests and the new power valve, dizzy cap and rotor arm have been fitted. The power valve has had to be ordered from the States so it will be a few days before it arrives.
I have also had chance to change all the plugs and leads for new again and the symptoms remain the same.
Fletch

 

Thank you for clarifying. I myself just ***umed a 4150/4160 Holley and I belive some other may have also, sorry for any confusion, TR

 

No worries when your head is not under the bonnet but half the world away spotting these things can be difficult.

 

So what happened?
Been a while

 

After all the messing, it looks like it was a combination of faulty ignition system (new sender and ECU fitted), fuel pump (new refurb Holley red fitted) and engine overheat. Engine has now got no thermostat and runs well. Looks like the rad (Rover 3.5) is a bit small combined with a relatively small engine bay caused engine to run hot, this was not apparent on the temp gauge because the sender is US spec and the gauge is Rover. This mis match means the gauge is reading cold when the engine is at about 80 - 90 C. The car also now has a back box/silencer (was running open headers) which seems to have helped.
I am now using the car almost daily and have just got hold of a 4100 shoe box carb from the US which I will get round to fitting when I have worked out the linkage for the AOD gearbox. Lets hope the carb change will not cause me more head aches.
Thanks,
Fletch