As Harvey says, start with the ignition system in good nick, so change the points, plugs and especially the distributor cap and plug leads. The latter because an old distributor cap is likely to be tracking sparks accross its surface (too many cylinders for the size of cap!) and the V8 is notoriously susceptible to poor plug leads. There is a very recent post on here about timing which discusses the two advance retard mechanisms on the distributor that is worth reading. Set the timing.
Next examine your throttle linkage. Go to Ian Wilson's site at Rover-Classics if you haven't got a parts manual (he has downloadable prints of all the pages) and check that you have all the rubber bushes and connection links etc in the system. It is quite common for the P6 to have "lost" a few of the bushes over the years. At best you will have lost half the available throttle opening between the pedal and the carbs, at worst one carb will open long before the other.
If all is well, next check that both carburettors reach full throttle simultaneously (engine stopped!). Adjust the likage between them if not. Remove the dashpot dampers and with the dampers out check that the pistons are free to rise and fall (engine stopped, finger down the induction tract). For really excellent results take the dashpots and pistons off the carburettors, remove the springs from both dashpots and dry the oil off everything. Now check that the pistons in both carbs take the same length of time to fall out of the dashpot. Swap pistons between dashpots until they do. Check both springs have the same free length (shorthand for the same strength).
Now you are ready to set the carbs with the engine running. You'll need a Gunson's Colourtune plug so that you can see the flame colour in the cylinder. Or if you're lazy two so that you can fit one each to a cylinder fed from each carb. Make sure that you can identify which carb feeds which cylinder by following the lumps in the inlet manifold. You'll also need a "stethoscope" to listen to the carb inlets. Any reasonably large piece of hose will do, I tend to use heater air ducting hose.
Set the engine to run at a fast idle, say 1200rpm. Set the mixture in each carb so that the flame visible in the colourtune is just going from orange to blue. Now listen to the "hiss" from each carb intake and adjust the slow running screw so that they both have the same hiss. Now repeat the misture setting. Repeat the hiss test. Keep going until you have both hiss and mixture correct at the same time.
Now check that operating the throttle linkage picks up both carburettors simultaneously. If it doesn't then you need to achieve a compromise between this test working ok and the full throttle test from earlier.
Next you can set your desired idle speed, again getting the carbs balanced using the hiss test.
Finally it is time to set the choke up. Adjust the linkages so that pulling the choke cable first picks up the throttles on both carbs simultaneously and then engages the mixture enrichment simultaneously.
Done!
And is it any surprise that you're often dissatisfied with the result when you've let a garage have a fiddle at tuning the engine! I can't see too many having either the knowledge or inclination to go through all that!
Chris
PS exactly the same procedure works for the TC as well.
Edited By chrisyork on 1201471087
, just need to sort out the air conditioning in a few months time. Thanks.