Single Lean Cylinder

[HuD 91gt]

Or, 5 rich…

I pulled the plugs today and noticed the cylinder closest to the firewall (6 or 1?), was much more lean the the other obviously over rich(Just black), cylinders.

What could cause a single cylinder to be quite a bit more lean then the others? I've recently replaced plugs, wires, points, cap, rotor, 1 of the 2 condensers on my automatic (Can't reach the other without removing the distributor and I don't have a timing light).

The plan is to adjust the valves, and then try and adjust the carbs, but I assume I have another issue before I tackle that one.

[HuD 91gt]

I was just searching online about general advice on this subject from other vehicles, and noticed someone mentioned if water was getting into the cylinder then it could cause this. Recently I noticed a small coolant leak on the back of the head between the block and the head. I guess a compression test is one of the next things to do.

[siteunseen]

That's #6, the one closet to the radiator is #1. I don't think that's lean, it looks really rich like it's not firing. Hook it in the plug wire and put it close to something metal and have someone crank the car over to se if a spark jumps. Could be a loose wire. Or a bad plug?

Or a bad wire, swap one over if it doesn't spark.

Edited May 6, 2014 by siteunseen

[siteunseen]

Wow! how'd I miss that. That's a great car you have there.

[240260280z]

If it is fuel injected, and siteunseen's great advice of checking for a spark shows a good spark then try swapping the #6 injector lead and # 5 injector lead. If the problem is with an electrical connection then it will show by swapping.

If your car has EFI then clean all electrical connections: http://www.atlanticz.ca/zclub/techtips/electricalconnections/index.html

[HuD 91gt]

Oops, sorry. I always forget to add the details. 1971 Datsun 240z with SU's.

The plug is very grey/white, even though the picture may not show it. The remaining 5 are definitely black.

I'll do as you guys suggested, hopefully your right and i'll update soon.

Edited May 6, 2014 by HuD 91gt

[HuD 91gt]

We have spark… Hmm

[240260280z]

Most of those plugs look rich with black soot.

[Zed Head]

Is there a problem with the way the engine runs? Didn't see any described.

The first thing described in the Tune Up chapter is valve adjustment. It seems like it might be the most difficult, changing plugs is easy and external, but I would guess it's #1 for a reason. Probably because it has the most effect if it's wrong.

I'm just like most people and did not adjust my valves until well after I had messed with everything else, when I first got my car.

[HuD 91gt]

Blue, I agree. The other plugs definitely show a rich mixture, but with the one that is quite a bit more lean, I was concerned before I try and tackle another issue.

Yes, the vehicle is still not running properly. Valve adjustment was next on the list, along with tuning the carb. I'll have to pick up a valve cover gasket before I dive in, as it looks like the previous owner used a liquid gasket of some sort.

I should probably merge all my topics as I work through all the bugs so people can get the whole picture of what has been done.

Edited May 7, 2014 by HuD 91gt

[HuD 91gt]

I should also note to Blue. The car is still not drivable, so I believe a lot of the carbon buildup on the spark plugs is due to extended idling, as the car has not been driving or been run for extended periods of time past idle.

[Zed Head]

Are you in Vancouver BC or Vancouver WA?

Read through some of your old posts and don't get a general picture of what's going on. In general, if things don't start working the way they should, getting all of the basics right is a great place to restart. Do all of the tune-up procedures and you won't have to wonder about them.