i decided to check the cylinder pressure on my 70 240Z.

all were between 150 to 155. which to me is great.

now the thing that has me bothered is that number 1 and 2 cylinder plugs where clean and just slighty tan and the rest were very dark tan almost black which i expected anyway because of it getting colder and me enriching the mixture.

what would cause the first to plugs to be so clean and the rest somewhat dark and looking as if they had been run rich. (as they should look)

any ideas thanks in advance

EZ

Hi EZ-E,

I'm wondering if the spark plugs match (same make and part number) and if the valve seals are all ok? Are you using oil?

I've heard from members on this site that NGK plugs are the best for the L24, L26, and L28 engines.

What is the pressure meant to be at for a L24? I measured mine and they were at about 110-120 ..........

EZ-E it sounds like you may have the rear carb just a bit too rich compared to the front one. By the color you describe it sounds like the front carb is just about right on judging by the plug color.

Alpha, you compression sounds OK. Remember, you can't really compare one engine to another if they have different heads, perhaps different piston types, bore size(one may have been bored during a rebuild), and the head may have been shaved.

If you see more than 10% difference between any tow cylinders then you are getting near time for engine work.

150-155 compression is excellent, I don't think you will get much more than 160psi without doing some engine mods...

the rest are all the same.

just the first two plugs from the radiator back. are light tan colored. all the rest are as if the car were running a bit rich.

as i said i did enrichen it a bit for the colder weather.

why only those two. the car is stock block and head E31, with ngk plugs, stock carbs, header and exhaust are the only mods oh and k and n filters not much.

oh and its not using a drop or hasnt in three oil changes