These are 1-6 front to the back in order. It seems like maybe lean to me except 2 and 3

1

2

3

4

5

6

They definitely look lean to me. Richen it up until they are tan in color. If you can't get them tan we will need some info. Carbs or F.I.? How many miles on the plugs? Plug brand and #. Assuming you're using round tops, How many turns down are your mixture screws? The reason I ask is it will also give us an idea if your float levels are close. If this a F.I. system I will leave that to others who are more knowledgable than me. As always dbl. chk. the basics, valve adj., timing, etc. I'm hoping as the mixture gets richer the plug colors will even out.

Mark in Portland

The benefits of having an air fuel ratio sensor. A more power from your engine will come from being a little on the phat side. Lots of questions to be asked about this reading. Not nearly enough info.

1972 240z SU carbs used colortune showed constant blue. I will try again maybe richen up more towards orange. Plugs are brand new BPR6ES-11 gapped .44 electronic Ignition. Not sure how many turns on the idle mixture just set it according to colortune. I haven't adjusted valves I just bought the car it has slight header leak so cant really hear the valves. I haven't set timing yet either not sure what to set that at. Thanks for the help

They definitely look lean to me. Richen it up until they are tan in color. If you can't get them tan we will need some info. Carbs or F.I.? How many miles on the plugs? Plug brand and #. Assuming you're using round tops, How many turns down are your mixture screws? The reason I ask is it will also give us an idea if your float levels are close. If this a F.I. system I will leave that to others who are more knowledgable than me. As always dbl. chk. the basics, valve adj., timing, etc. I'm hoping as the mixture gets richer the plug colors will even out.

Mark in Portland

I have heard that reading plugs is useless with unleaded fuels... I use A:F gauge.

conedodger

What color are your plugs using an A.F. gauge? Mark in Portland

1972 240z SU carbs used colortune showed constant blue. I will try again maybe richen up more towards orange. Plugs are brand new BPR6ES-11 gapped .44 electronic Ignition. Not sure how many turns on the idle mixture just set it according to colortune. I haven't adjusted valves I just bought the car it has slight header leak so cant really hear the valves. I haven't set timing yet either not sure what to set that at. Thanks for the help

Costjo-

You got things a little backwards - get a solid tune up before you start trying to look at your plugs and listening to your valves. Get a valve adjustment compelted, then do a complete tune up including timing setting. Get all the majors completed and then start with your SU adjustment. Reading plugs should be last on your list. The first thing on your list needs to be to read as much as your can if this is your first Z. There is a lot of knowledgeable folks on this site that enjoy sharing their knowledge, but you got to help yourself first by digging into research (just like all of us have) to learn how your Z operates (or find a skilled mechanic).

Keep us posted with your results.

Too Lean

Too Rich

Just Right

The fact 3 runners share 1 carb means the balance of fuel may not be even for all 3.

That reminds me of "This is your brain..............this is your brain on drugs" with the frying pan back in the 80's. Great Marsh-mellow viewpoint...........never thought about it, but it fits!

Costjo, all your plugs are too lean, except for 2 and 3, which might be WAY too lean. Once the mixture leans out enough, the cylinder starts to partially misfire, which can make the plugs look as though the mixture is too rich. You might have a vacuum leak that bleeds air to #2 and #3, for instance if your intake manifold isn't seated well.

1972 240z SU carbs used colortune showed constant blue. I will try again maybe richen up more towards orange. Plugs are brand new BPR6ES-11 gapped .44 electronic Ignition. Not sure how many turns on the idle mixture just set it according to colortune. I haven't adjusted valves I just bought the car it has slight header leak so cant really hear the valves. I haven't set timing yet either not sure what to set that at. Thanks for the help

I would fix that header leak first. Set valve clearance also, set timing to around 15 degrees before tdc with vacuum advance disconnected. You should not mess with the spark plug gap, I did that last time, and the engine ran really bad, then I checked the manual and it says around 0.8 that's the standard factory gap. Leave the gap as it is out of the box don't mess with it. I would recommend B6ES not BPR6ES as the manual recommends. I've found the standard plugs run better. Also watch if the plug says made in Japan ( usually black letters ) or made in France ( blue letters ), you will need the made in Japan, somehow I found problems with the made in France ones.

I found there's not much to adjust to SU's, the main mixture screw is the most important, if you can't get them right to need to either be rebuild or changed with another good working pair. I had the same problem with mine, they where just worn out, causing vacuum leak on the butterfly shaft also.

Edited February 12, 201411 yr by bartsscooterservice

I'm with Mitchell on this, they are too lean. I run with a wideband O2 sensor and have tried to run as lean as possible to be around the optimum 14.7, but it's just a reference number for me. I believe these engines run best a little phat as stated. The marshmellow should be that nice tan color. I think you can even hear the difference between too lean and just right, and you can definitely feel it mid throttle. But as stated above, get all parameters -especially the exhaust leak-fixed and right and then start squeezing in some more juice.

I believe the .044 gap is okay for the Pertronix, maybe back out a few thousands .042