Jump to content

IGNORED

Single Lean Cylinder


HuD 91gt

Recommended Posts

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.

post-30294-14150828444845_thumb.jpeg

post-30294-14150828445264_thumb.jpeg

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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 by siteunseen
Link to comment
Share on other sites

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

Link to comment
Share on other sites

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 by HuD 91gt
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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 by HuD 91gt
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Vancouver BC. I'm slowly making my way through the tune up procedures. After installing all the ignitions points etc the car was idling very nicely. Unfortunately this seems to have changed as it sat for a week or two and is no longer the case.

I'll try a valve adjustment and see where we sit. I just ordered a Haynes manual as the FSM doesn't seem to explain how to do things, but rather how things work. I think the combination of the two should help immensely. Thanks for everyones suggestions.

Link to comment
Share on other sites

Doesn't the '71 have 2 choke levers? Are they both pushing and pulling the cables completely? Here's how I learned to do the valve adjusting, PictureTrail: Online Photo Sharing, Social Network, Image Hosting, Online Photo Albums. Doing them cold will get you close enough for your 1st time. But you gotta go back and do the "fits, or doesn't fit" when the motors hot some day. That Haynes manual will make a good beer coaster while you're reading this forum.

Link to comment
Share on other sites

I ran into a similar issue where I thought number 3 cylinder was running rich (when compared to cylinders 1&2). Turns out I had a manifold gasket leak at the intake manifold for cylinders 1&2 which leaned up the mixture for those cylinders. Since tightening up the manifold nuts, I now have much more consistent plugs across the first three cylinders. The intake runners for cylinders 1&2 and 5&6 are "siamesed" so only way I could see this being your issue would be if the rearmost intake manifold bolt was loose or perhaps you had a manifold gasket leak for the #6 intake runner.

The remaining plugs do look rich. Suggest you clean the plugs and reinstall. Then check that the chokes are fully off (i.e. push up on the bottom of the carb needle housing to ensure that they are fully closed). The P.O. for my Z had installed bike cables instead of solid choke cables and the chokes would not fully close without assistence. If chokes were fully closed, suggest leaning each carb by 1/4 turn of mixture nut. That said, you really can't get an accurate reading on the plugs without driving around for a period of time, with the engine under load.

Link to comment
Share on other sites

2 choke cables would definitely make sense. But I am missing one in the cabin, but there is a spot next to my choke(On the centre console) which looks like it could house another(I was always curious what it was for. But besides that, the single choke lever I have does indeed actuate both chokes(He must have put in a linkage from another motor?). After advice from other forum members, I had to clean up that area so the chokes would spring back up. The car ran great. Maybe they are sticking again! I didn't even think of that.

Over the next couple days i'll try and check the manifold too. Thanks for the suggestions guys! Also thanks for the valve adjustment link. I also found a video tutorial of a guy doing them on a L20, (maybe L16) so I'm thinking it will be pretty simple by following that. I will update once i'm back home, for now im on the road for the next few days.

As for doing the valve adjustment hot or cold. I don't see any harm in doing them up to temperature as the car will idle well enough to get up to temperature. But it all depends how fast I can do the adjustment if it will stay hot. Ha. How quick do you need to accomplish this task?

Edited by HuD 91gt
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Who's Online   1 Member, 0 Anonymous, 59 Guests (See full list)

×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.