Ideally yes for the meter as this accurately captures the readings.
The Colortune has a clear spark plug that lets you look into the combustion chamber while the engine is firing. The colour of the combustion flame tells you if the mixture is correct. With the carburettor mixture screw you can then adjust the flame colour to get the correct mixture.
Just found their u tube promo
Just for clarity, the OEM plugs were never NGKs but were Champions. In the case of the SY2 cars they were either RN 14 Y or XN 14 Y with a gap set to 0.03 in/0.76 mm. I don't think this changed from the SY1s and it's documented in the Owner's Handbook and, I believe, the workshop manual. NGKs are the "accepted standard" now and Crewe issued a service bulletin stating that BPR4EVX were suitable for all V8 engine cars. Some people have gone to the iridium plugs, which I think are real overkill for the older carbed cars, and NGK recommends the V-Power line for the SY series cars.I did some search, and found the OE spark plug would be NGK BPR5ES, which is 14mm thread size.
BTW, what's the difference between BPR5ES and BPR5ES-11?
I'll let someone else cover your first questions since this isn't territory I've covered myself.Also, the cold start idle rpm is just around 200-300, then the rpm would gradually go up to 600-700 as the car warms up. I remember the car used to cold start at 500-600 rpm and then gradually go up to 1100-1200, as the fast idle mechanism regulates. I did not tamper with the fast idle mechanism since I got this car. Something wrong with this symptom.
I'll let someone else cover your first questions since this isn't territory I've covered myself.
However, what you describe as the idle behavior on your car is, as the saying goes, bassackwards. When you set the choke the fast idle cam should also be set. When the car is started cold the mixture should be enriched by the choke and the amount of fuel being fed through increased by the fast idle cam so your starting idle should be far faster than your normal "warm resting idle."
You can turn off the fast idle cam by giving the accelerator a quick punch with your foot to release it. The idle speed should then decrease though if the car is still cold and the choke is still closed it will remain faster than a warm resting idle.
You shouldn't have a slow idle with gentle climbing on a cold start if all the bits meant to assist with a cold start are functioning as intended.
If you hear hissing you've got a vacuum leak. Definitely nip that in the bud and hope that no one has adjusted the car "to make up for it."
These days most people replace vacuum hosing with black silicone since it holds up so much better to heat over time and doesn't become brittle and/or shrink. Any time you are replacing vacuum lines only do one line or line segment at a time!! Problems can arise by your either introducing a leak that wasn't there or eliminating a leak that was that others have tweaked to "work around" not knowing anything about vacuum leaks. If you do more than one segment at a time it is nearly impossible to determine where the culprit lies. If you start the car after each segment and things stay the same you know you're no worse off and probably haven't either induced a problem or solved one, either.
One way to check for vacum leaks is to spray carb. cleaner at any suspicious looking joints or pipes. If the car stumbles, you have a leak.
I have both a gas tester and a colourtune and the colourtune is the best way as you see an immediate change when you make an adjustment. For quickly checking a car I use the gas tester, but all adjustments are made with the colourtune, and I trust that more than the analyser. Apart from anything else on cars with dual (or more) carbs it's impossible to know which carb to adjust with the analyser. If your car is running rich it might be 'hunting', maybe try checking the mixture now, and correct it if required, then see if the vacuum gauge still fluctuates. I always find it's best to go round in circles; set timing, then idle, then balance, then mixture, then check timing again, then idle etc until it's all correct. No point trying to make one thing perfect when other things might be wrong, and adjusting those will have an affect.
Are you definitely turning the right screw. There are two - the volume screw and the jet adjusting screw. I am sure you are, so I will continue/
Remove the 4 setscrews and pull off the vacuum chamber (figure 12, chapter K in the SY1 workshop manual). Remove the long piston spring and pull out the piston. Make sure you do not mix parts between the two carbs and never rest the piston on it's side as it may bend or offset the needle.
You will now be able to see the jet. With the adjusting screw fully loosened, the jet should be proud of the bridge piece by about 1/8". As you turn the adjusting screw clockwise the jet should move downwards until it is about a quarter of an inch below the bridge piece. If the jet does not move then cleaning may free it off. Another possibility is the spring holding the jet in position may be tired and not exerting enough force to hold the jet firmly in place.
If everything looks ok and the jet is moving up and down with the adjusting screw, run your fingers along the piston needle. Check for any steps or ridges in it denoting uneven wear. Even if you detect no ridges, it may be the jet and needle have worn smoothly and therefore causing the rich mixture.
Ultimately, recon kits are cheap, so it may be worth just reconditioning the carbs and fitting new needles.