I installed a new cam in my 351w this weekend. I installed new plugs during the process. After I did a 25 minute break in I changed the oils and drive it Around town for maybe 20 minutes. I pulled the plugs and was surprised to see this. They look a little lean but I'm not exactly sure. What do you think?
cant see any sign of heat (excessive), second from left slight oil marking, new lumpier cam? probably slightly lean but I haven't done this much since lead was taken out, used to be a good colour chart by Champion?
The 2nd from left is an older plug because the parts store only had 7. I'm trying to learn all this tuning so I can keep it running right and not blow it up. I just don't have enough experience to know what I'm looking at or for. It's not as easy as I thought.
Like squirrel says, plugs are hard to read today. They do look a little on the lean side to me, sometimes when you are cruising about 70 mph and you hit it hard, if it spits back through the carb, then you know you are on the lean side, I would go up 4 intermediate jet sizes if you are using a Holley and see how that does.
I would just run it the way it is, if the jets in the carb are the ones that came in it stock. If you don't know what the jets are, then get a wideband O2 sensor and see what it does. It's kind of amusing to see what the AFR is with a good running Holley carb
Jetting is 66/72. What gets me is the dang thing is only gettin 8.5 mpg. I jet it more I'll be investing in opec lol.
usually jetting won't affect mileage a whole bunch. Holleys tend to run a bit rich most of the time, but yours is apparently not flooding out, the plugs are not sooty. If it has a lean surge or sneeze, then you probably want to richen it up, but you didn't mention any driveability problems.
I'd put some more miles on; as long as it don't rattle or over heat in normal driving run it around...When you get some heavy foot later after 500 or so miles then can play with carb if necessary..Heads?..Cam? .Have fun..
After I looked at the plugs I was kind of nervous about driving it. I didn't want to lean it out and hurt it. I have been pretty easy on it after the cam swap because it only has 20 miles on it. I appreciate the info you guys have given me. I will take it easy on it till I get some miles and then see how it runs.
yep, not as easy as it all seems - along with setting carb & timing need to consider more details on plugs www.hotrod.com/how-to/engine/116-0703-spark-plug-guide/ - the modern spark plugs, such as Autolite 45, do not have equal heat ranges that previous, such as Autolite BRF42, do - the last digit in an Autolite current part number represents the heat range within a plug family - not the individual plug
This true reading plugs is an entirely different game then it once was. One thing to think about is that unless you are running really fat your plugs are going to take a while to stain. In order to see what is going on with them you have to look way down at the bottom of theof the porcelain. They make a tool for that most resemble this: They are lighted and normally have a magnifying gl***. There is also a proper way for reading plugs if you are a tuner that most don't practice. You run the vehicle at the intended RPM, for a short way then you shut it down and throw it into neutral so that it does not load itself at shutdown.
Learned to read plugs as ****** says-run it down the road-kick into neutral and shut it off and plug a plug or two.
THIS!!!!!! Start with fresh plugs,make a wide open 1/4 mile p*** and shut it off WITHOUT closing the throttle! Look at the BASE of the porcelain and there will be a soot or greyish ring. I sometimes cut the threaded part off the plugs to get a very good look at them.
Something else interesting about plug reading is fuel distribution. An SBC for example will almost always read fatter on the rear cylinders on the drivers side. it has as much to do with out of sequence firing as it does with intake design. The 5 and 7 cylinders are not far enough apart in the firing order and unless you have a 180 exhaust system they will not scavenge each other well.
I've always wondered how anyone can get much info from plugs in a street car....was it rich when it was idle? when you were cruising? I know you weren't under full throttle conditions long enough for the plugs to tell you anything about that, unless maybe you're running nitrous and it went lean and burned off the ground strap
It's really hard to tune a carb now on the blend of gas @ the pump, especially 10% blend . It will give You false readings by just Looking ,, ( Plugs) My self I spend Many hours tunning a carb , ( way more than other do , )) I really tune a carb , I now deploy A Big 5 inch vac gauge 0-30 Larg tack Wide band 02 gauge And A GO-PRO Camera, But I am A Tunner , looking to get the most out of my set up , Where most would just throw Jet's in & call it a day!
When I was tuning a little road race car we read the plugs at the most common operating RPM for a given track and adjusted accordingly. There was more to adjustment than just the plugs and intake charge but that's probably way beyond the scope of the discussion isn't it. For drag racing it is easy, WOT for a quarter mile then shut it down and tow it back to the pits. For a carbureted street motor it is a little more difficult, they still don't make a carb that will run flawlessly at all throttle positions. On my bike I do most of my running on the highway so my carb jetting is setup for highway running it runs a little fat around town but such is life. For an around town vehicle I would adjust things to run in the low and mid range mostly, unless I was one of those guys that thought that high rev cruising was a rush and kept it revved against the red line all the time.
I ordered +2 and +4 jets for front and rear. I am going to put some highway miles around 2500 rpm the shut it down and check the plugs without letting it idle and see where it's at. Then I'll bet if it stays white like that.
from the comments above it would appear that reading plugs is a lost art..... timing (bluish mark) is very close to optimum, Your center porcelain is "coloring" and showing a gray color. I would run this combo again and check it as described (shut down at 2500-3000) You may find this is too rich....
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