jmead Posted August 22, 2003 Share Posted August 22, 2003 I know you can get a general indication of how a car is running by "reading" the spark plugs. Unfortunantly, I couldn't find any sites with a detailed explination of just what to look for, so I'll let the experts at HybridZ take a look. I'm not sure exactly how old these plugs are, but they probably have around 3k miles on both sets. They are layed out such that the plug furthest on the right was the plug closest to the driver. This set it from a 1970 240z with dual SUs. I'm guessing this means the carb towards the driver is running rich, and the carb towards the front of the car is running lean? Any simple way to adjust this? (links maybe). My manual covers carb disassembly, but not tuning. This set is from a 1976 280z, fuel injected. I'm guessing this means that the engine is running rich in general? Any way to correct this? The car is stock, I haven't messed with the injection to cause it to go out of tune. Thanks for any suggestions, ideas, professinal opinions, etc. Sorry for the large pics, but I wanted the plug ends to be easily visable. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted August 22, 2003 Share Posted August 22, 2003 First I would strongly recommend double-checking the miles on those. I would say it is unlikely that you should have nearly those kind of results after only 3000 miles. For the top ones you are pretty-much correct. The left carb is running much too rich (the black plugs) and the right carb is running quite lean. Those 6 plugs look like the timing may even be off as well because you have the orange-ish coloring. (I believe this can occur if firing too soon as well as too late). Since there is such a difference between the first 3 plugs and last 3 plugs I would say you probably need to balance the carbs. (carbs being off balance might also cause some orangeness as the lean cylinders will be running hotter). As for the bottom plugs from your FI engine those are pretty good, a little rich. Slightly greyish deposit is what you should be seeing. (Like I said though, shouldnt be that much until many more miles, probably closer to 7500) Of course, if you live in a higher elevation I believe it is normal to have to change the plugs more often. As far as helping with the richness on the FI I would try to open up the intake and see what you can do to get more air in, preferably cold air. Also remember that richness is not specifically regarding the air/fuel mixture. The deposits are specifically from incomplete burn, whether that is from a rich air/fuel mixture and/or the result of bad burn is another topic. I'd recommend running some fuel with some good deposit removing cleansors (Chevron's Techron or similar) in addition to trying to get both engines to breath better. Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted November 8, 2003 Share Posted November 8, 2003 You can find a Colored Picture guide of "Reading Spark Plugs" on the back of the book cover to Chris Jacob's book, "The Doctor's Step by Step Guide to Optimizing your Ignition" w/a 1984, 1986 Copywrite. His book has since be renamed, it now goes by the title, "Performance Tuning Systems. The newer book also has a guide to reading spark plugs except it is not in color: it is in black & white w/a good discription: you will find this chart in the middle of his 1999 Copywrite book. Some of the cheapy repair manuals also have this chart in the back. Sometimes they are colored and sometimes thay are in black and white. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
datsunlover Posted November 11, 2003 Share Posted November 11, 2003 Don't know if all you folks in the States have these, but up here in Canada there is an auto repair "do it your self" series of books (similar to 'Chiltons') called Haynes. Every Haynes manual has a page in it (color too!) showing comon spark plug problems and conditions. If anyone wants this picture, and can't get access to a Haynes manual, let me know and I'll scan it for ya. Quote Link to comment Share on other sites More sharing options...
Dacelooper Posted January 21, 2004 Share Posted January 21, 2004 most detailed images i've ever run accross. http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 18, 2004 Share Posted February 18, 2004 wow... someone really spent some time with all those pics, great link! -Ed as for your carbs i would do what you originally thought, but the EFI i would just adjust the timing a little, put in clean filter. Those arn't dirty enough to worry about, the EFI on the Z carbs plugs real easy at idle. If you only drive around town locally, you probably never run it high enough to clean em. Quote Link to comment Share on other sites More sharing options...
74_5.0L_Z Posted February 26, 2004 Share Posted February 26, 2004 Its been a while since I've adjusted the SUs (Mine has had a fuel injected 5.0L for 4 years). But to fix the top plugs, I'd lean the SUs out and balance them. Do you have a Unisyn tool? If not then get one. Do you know how to adjust the SUs and balance them? How many turn out are the big adjusters on the bottom of the carbs? What fluid are you running in the dampers? What needles are installed? As a base line, I always run the bottom adjuster all the way in then backed them out 1.5 turns. Quote Link to comment Share on other sites More sharing options...
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