Ddgonzal
I was going to say that 1200GXman has a genuine GX engine with the twin Hitachi's This is an excellent setup as i was able to pull high 30's per [imperial] gallon anytime i took my GX powered 1000 sedan out for a drive.
I got better than 40 mpg when driving for economy at an average of more than 70 mph on a 250 mile run one night when going to the Bendigo [Victoria] swap meet.

I got better than 50 mpg when i drove for outright economy when i went to the Ultralight fly-in in Holbrook [NSW] about ten years ago. Yes, it was a slow trip. The GX is a superb engine. Plenty of pep, plenty of economy. It's all in how you drive it.

1200GXman
Try setting the plugs to .9mm & see how it runs. Put your hand on the coil at the end of a drive to check the temperature. If it does not raise blisters on your fingers, then it has not overheated yet. If you get any misfiring, think about using a 'sports' coil. Bosch marketed the red coloured GT40 coil [40,000 volt max output] in Australia & these provided more voltage when it was needed.

If all goes well, then try 1mm & see what happens. If you suffer misfiring at full throttle & full load, then you need either more volts [sports coil] or a smaller plug gap. The bigger the gap, the higher the voltage needed to fire it. The higher the compression pressure, like at max torque, the higher the voltage needed to fire the plug. Continuous high outputs build heat in the coil. Excess heat kills coils, so a sports one really is a good idea. Make sure that you get either the resistor type [GT40R] or the regular non resistor type, whichever is correct for your car.

Lemonhead

Congratulations.
Let us know what the dyno figures say.
I am VERY curious.
What setup is your engine again? I cannot remember.

DDgonzal.
I have the Hitachi SU's.
December I am going to remove them and clean them up inside and out.
Going to tune them as best as I can and maybe slightly leaner.
Going to make my gap then 1mm instead of the standard 0.8mm on the plugs.
Is 1mm a bit too large?

Yes interesting topic relating to the more finer details of good engine tuning, thanks for the input.
New head is on! Idles very smoothly on 1000-1100 rpm, idle noise at the exhaust sounds very nice.
Off to Mike Vine dynotuning on Tuesday next to see the difference the new head/roller rockers have made to the power output, pre-dynotuning its wicked!!
An idea of what the roller rockers have done for valve train: Lift at valve was just under 12mm, now just below 16mm (later dimension was done pretty crudely, will do more accurately when i take the tappet cover of to re-check tappet clearance)

1200GXman, you can always replace standard plugs with platinum equivalents, for any engine -- even a lawn mower.

To set your expectations, they are not going to increase your fuel economy over a new set of regular plugs.

To increase economy, use the stock Hitachi carburetor instead of a weber. If you have a weber, jet it slightly lean all around. This is where a larger gap will help, to fire the leaner mixture. With stock ignition, I recommend 0.035 inch gap (8 mm is the Nissan spec, which is only 0.030). This bigger gap should smooth out the idle on a stock A12 just a tad.

This is something I am also interested in.
Given the following information can anyone give me some advice? :

I have recently installed a Pertronix Ignitor in the place of my points breaker systems.
I am using the stock coil still.
On the advertizement they say it provides better power to the spark plugs.
Can I install the plugs you guys are talking about that will provide better spark?
Or must I keep using the standard spark plugs that is in the workshop manual.
What about the gap?
The standard gap that I am currently using is 0.8mm.
Why I am asking is I am after even better fuel economy.
Anything that can improve it I want to try.

Can you believe it.
I once wanted to do performance improvements to my A12 now I want to do economy improvements.

Many thanks.

Quote: Actually, they do work better, as well as wear much longer.
With a much finer center electrode, they need less voltage to fire a spark across a given gap at a given compression pressure. This means that you can run a wider gap at the same voltage requirement as before.
Alternately, if the ignition was breaking down at a certain rpm level, it should run better at the same rpm if Platinum or Iridium plugs are used with the same gap, due to the lower voltage requirement.

How much lower? I don't know, but, as i wrote earlier, i will be experimenting with gaps to try & find the widest "practical" gap that i can use long term in a street engine.
My 9.something to 1 compression should allow a reasonable scope here.

All i know about the engine is its S13 and eng# 240964W if that helps you identify what year. I guess it would be 89 to 90 model

The gap depends on the igntion system. Which one do you have? If it's a stock system, what year and what car model did the CA18 come out of?

Most of the '80s high-energy stock systems use 0.044 to 0.053 inch gap. I would say you can't go wrong with using 0.044, if you cannot find the exact spec for your system.

Can anyone tell me the recomended gap size for a CA18DE, As im putting new plugs in at the moment. And ive alredy done a search.

yes it is fuel fouling...yes it does run rich and with no choke, so what i may be hearing is put up with it or run EFI