As I recall, from our '72 Newport Royal 400 2bbl, the factory spec spark plugs were Champion J-13Y non-resistor plugs. The prior 383 2bbl plugs were J-14Y and most of the B/RB 4bbl plugs were in the J-10Y to J-12Y range. So, to me, most anything in the J-12Y to J-14Y range would probably work well. As long as the engine is not using oil (1000 miles/qt or less miles/quart). The J-13Ys usually "patterned" the center ceramic in a light beigh color with minimal deposit accumulation. Recommended plug gap is the normal .035", although easing up to about .040" can work too, if desired.
Considering the access to those spark plugs, it MIGHT be advisable to find an equivalent in either platinum or Iridium plugs. Getting to #7 and possibly #5 can be best done from underneath. Just watch out for the hard plastic water shield for the starter attached to the stub frame!
As for the ignition cap, it is not usually a maintenance item. Unless it might crack or have some carbon tracks between the inner terminals. If there might be some accumulater deposits, then get a flat screwdriver and scrape them off to leave exposed metal. Same with the end of the rotor. IF you might decide to replace it, getting a tan cap would look the best, to myself and many in here. The factory caps had aluminum contacts, but the "optimum" contact material would be copper. The aluminum worked just fine for Chrysler and other OEMs.
As for fuel economy, ONE thing NOT to do is to over-tighten the air cleaner wing nut! Why? The air cleaner stud attached to the center of the carb. That casting looks substantial enough to do what it does, BUT over time, the torque applied to the wing nut will exert an upward pull on the stud, which can also pull that casting "up" in the middle. This is also in the same area which seals the rear of the float bowl between it and the carb venturi area. When that seal goes away, it also kills the vac signal to the power valve, which means the carb is running "full power mixture" all of the time, which on our '66 Newport 383 2bbl, meant about 10mpg no matter what. The '66 had a Stromberg WWC 2bbl and the '72 had the newer Holley 2210 2bbl, which is of the same construction and design as the Holley 2245 2bbl on your car (the difference between the 2210 and the 2245 is that the 2245 is an "EGR carb" and the 2210 was not).
The Holley 2210 carb is a newer design (for back then) which means a very responsive accel pump and more efficient-design carb venturis, which was necessary for tighter emissions standards. When I replaced the Stromberg WWC on the '66 with a '70-spec Holley 2210, I could tell it was running more efficiently by the way it ran, which was good. The first trip I made from Lubbock, TX to DFW at 55mph, resulted in right at 20mpg on the road. Which tended to coincide with the Lubbock Chrysler-Plymouth dealer recorded on a '74 Chrylser Newport 400 2bbl in one of their highway fuel economy tests (20.33mpg).
In real world use, our '72 Newport 400 2bbl usually averaged about 13-14mpg in the way it was being driven. Small town city driving and some rural highway driving each day. On longer Interstate highway trips, it would usually do about 15mpg at 70mph speed limits. In general, the low-compression 400 was about 1.0-1.5mpg less than the '66 Newport 383 2bbl with one point higher (9.2 vs 8.2) rated compression ratio. I need to note also that this was back when "gas was gas", unlike the current ethanol'd blends we now have. E10 is supposed to yield about 6% less mpg than E-Zero. Also, at those times, the cars had fiberglass-belted bias ply OEM spec tires, rather than radials (which might yield a few more % of highway fuel economy).
Air cleaner wing nut torque? In prior times when the top of the air cleaner was a big-upside-down type of item, you could not see if the top was fully compressing against the air cleaner element. So, "tighten it down good, until you see the top compress against the element. In the later designs, with a separate flat top, this is much easier to determine and feel. To me, just enough torque to see the top move down a slight bit, snug but not more than that.
IF the carb top has warped, I believe that
@saforwardlook has found the Autoline (carb rebuilders) are aware of this situation with the Holley 2210-family carbs and has adjusted their processes/procedures to correct for it. Chrysler did put out a factory "bridge kit" to address this issue, back in the middle 1970s. It worked on our '72 Newport 400.
You'll also notice on the tune-up specs decal on the core support, that the base timing (at least on our '72 Newport 2bbl) was 7.5 degrees BTDC plus and minus 2 degrees. Of course, 10 degrees worked well for the '72 Newport. Whereas the '66 Newport 383 spec'd 12.5 degrees BTDC and as we normally ran "ethyl" in it, I eased it up to 15 degrees BTDC with no issues (with the OEM-spec distributor centrifugal and vacuum advance settings).
You might also notice that the a/c compressor runs even with the inside control "OFF". This is normal on those cars. PM me for details.
The 400 2bbl, even back then, was a credible performer which would return decent fuel economy (for back then). The main issues were its lower compression ratio, when compared to the prior 383 2bbls, in its performance and fuel economy. ALSO, the Fuselage cars were about 200lbs heavier than the Slabs, which did not really help anything either, performance-wise.
Welcome and enjoy!
CBODY67
