Op here, not showing off, genuinely curious and trying to not have to pull this motor. It's been about a month, time to take a look at these plugs again. I'll try to remember to kill it on the freeway on my way home from work.

 

A lot of people would love to have plugs that look like that. But, I wouldn't run them like that unless I was already very experienced reading plugs. The nice thing about a wideband O2 sensor is it will tell you instantly if the AFR is dangerously lean. It's OK to jet down pretty lean for an economical cruise on flat ground, though it's very important not to ever go lean under power or acceleration. Think what happens to the flame of an acetylene torch when you crack open the O2.

Is that a fairly high heat range plug you're using, that may confuse things. What scares most people is the absence of a tan color on the ceramic, though that isn't really what to look for. Modern gasoline shows little. The base ring shows jetting, which may be real good. But deep inside the plug, where the ceramic transitions to the shell, is the wide open throttle AFR indication, called the "fire ring". A lot of guys will sacrifice and cut plugs open to get a better look at it, stuff like that. If your truck isn't surging or misfiring, running hot, etc on the highway you're OK on jetting.

Wide open throttle fuel mixtures are a different deal, a different carburetor circuit, and maybe the AFR is OK, though ... maybe not. It is very common for carb tuners to jet down quite a bit and open up the PVCRs to richen up the wide open throttle mixture in response. But I'd want to see the AFR in black and white before running plugs that looked like that.

 

Just me, but those plugs look too lean with no deposits on them. But your being in Kalifornia, that might just be the fuel there too. You running E10, 15 or what ?

 

Baddad, the last set of pics are a month and a half ago. I haven't looked at them since then. I'm going to try again to remember to cut throttle on the freeway and pull one or two. Failing that I'll pull them at work today.
For fuel I'm running arco 91 octane and aparantly California has no labeling requirements under 10% with the best guess I can come up with in a few minutes on Google is 5.7% average in crazyfornia.

 

Damn, I'm surprised they let them sell fuel with less than 10% ethanol. Over here, anything under 5% can be sold as conventional gasoline (straight gasoline) I run about a 50/50 mix of 93 Octane E10 and 91 Conventional in my 331. This is carbed (3x2) and sparked with a stock Duraspark unit on a 77 Comet. My plugs look like new after a year's time, but with black or dark grey fire rings.

 

Hey guys I'm going to hijack my own thread and hope you get a notification. I finally added the PCV valve that the PO didn't put on. Now I'm having hot start issues. Not hot but operating temp. I haven't tried a cold start yet and it seems to be fine once started. Seems to not get enough fuel,( too much air) while cranking. Any ideas?

 

hey guys, been about a year since I started this post. Pulled a plug today in a maintenance check and thought about this thread. I don't know the mileage when I started the thread, but I've been driving a 40 mile round trip 5 days a week for a year for the most part and haven't really touched the engine except for oil changes and carb adjustments since then. So, here are the same plugs today.

 

Those look good, but are those the stock heat range plugs?

They look a little toasty maybe, but I don't know for sure. One thing to look for is a temperature band or color transition on the ground strap, ideally about halfway up, right at the bend is about right. Ideally a spark plug reaches a temperature just high enough to burn off deposits, but no higher.

If those are hotter than stock issue plugs, I would not jet up just to make them show color, I'd first run the stock heat range plugs to get a baseline. Inspect them and jet as required. The stuff I've read claims it is safer to start out with a "cold" plug and work up from there, spark plugs are inexpensive, and the worst thing that can happen with too cold of a spark plug is fouling but, too hot of a plug can cause detonation and engine damage.

 

I agree, they look a little hot/lean... But maybe more lean than anything... the deposits on the insulator nearer the tip (to me) looks like the plug is near the right temp, just that there's nothing to get it dirty

During that drive, what RPMs are you seeing? Without an overdrive, you'd be amazed how squeeky clean things can get while running at 70MPH...

 

I have no overdrive so I'm running between 3000 and 3500 rpm. What would be the correct heat range plug for my 352? Should I do a full throttle 1/4 mile then put out the fire and pull a couple plugs? I can manage that on my way to work tomorrow. I assume that I have a spark plug socket in the truck.

 

The operator's manual will list the correct plug. What are you running right now?

One thing though, modern electronic type ignitions are a fair bit hotter than the points & condenser systems that were used in the 1960s. This is a good thing, but they used a plug with a high enough heat range to reduce fouling in typical stop and go driving and short trips. The stock heat range plugs were probably too hot for summertime extended highway driving. Most people couldn't be bothered swapping plugs around, then or now.

Plug reading is hard with modern gasoline, it does not "color" the same as old school gasoline, but there are some good web pages that illustrate what to look for. Each carb circuit is tuned independently.

It's possible for example you are jetted perfectly, though too lean on wide open throttle. Idle time will load up the plugs, this is why a "throttle chop" is done, pull over to the side of the road and check. The base ring shows jetting, deep inside the plug shows wide open throttle. Heat range (and ignition timing) shows on the ground strap. This is why it's important to use a stock or middle heat range plug, to get a baseline first, for carb tuning.

The general idea being for an example, if the spark plugs are fouling out badly, the remedy is to correct the AFR provided by the carb circuits, not try to install a hotter plug. A wideband O2 sensor takes a lot of the guess and by golly out of the equation.

In your situation here it might be too lean at wide open throttle - but you don't want a super hot plug skewing your analysis. Jetting up isn't the remedy for a lean power circuit. Very misunderstood topic. David Vizard has a book out on carburetor tuning that is really good, it's excerpted online.

 

Tedster, Did some learning today. The plugs that are in it, Motorcraft BSF42CA, are a direct cross to the BF42 that the shop manual recommends. I learned that heat range information is not that easy to come by, but the next cooler plug is a Motorcraft SP414. I have a set coming tomorrow. I also learned this morning, after accelerating at full throttle in high gear from 60 to about 100 MPH, cutting power and coasting off the onramp, around the corner, and to a quiet street with shade trees, that I didn't have a 13/16 spark plug socket or anything else in the truck that would loosen a plug. I'm going to remedy that tonight and try again tomorrow. Then I'm going to put those plugs in.

 

Haha!! Yeah ... "best laid plans .." and the rest if it. The Vizard book is called something like "tuning and modifying Holley carburetors", goolag has quite a few pages of it excerpted. I would never have run spark plugs that even looked a little bit lean, not before using a wideband O2 sensor. Otoh when I bought the '64 lo so many years ago the plugs were dripping wet and looked like they'd been sprayed with black paint.

With a wideband sensor backing me up I didn't worry so much and have since learned to read spark plugs, at least a little. There is a whole bunch that can be learned looking at plugs.

The important thing to always remember is never go lean under load or acceleration, under power. I have the tiny 2 bbl Autolite in my slick tuned for a pretty fat 12.5 AFR in the power circuit and about 16 AFR at steady highway cruise. If a carburetor is jetted too lean in the highway cruise circuit it will surge or misfire, but if an engine is lean under acceleration or load it might not be noticeable - till something burns up, like exhaust valves. Increasing jet size will most definitely compensate for a lean power circuit, but it will overall then be way out of calibration, too rich on the highway. Getting the carb tuned "just right" in the different circuits makes for easy starts hot or cold, crisp idle, no bogs or hesitation, good power, and an economical cruise.

 

Well, I have been driving the **** out of this thing for a year now and I guess if it was too lean in the power circuit I would have broken it, either burning a valve or holing a piston. I have been considering an AFR setup. I'm thinking maybe a diagnostic ty[pe that I can use on other than my own truck. I am a mechanic by trade and it would probably be a worthy purchase for my (*overstuffed) toolbox. most of the ones I have seen look like a permanent installation, like a dash gauge. I guess I haven't put much time into shopping for one yet. Oh, I did ask the SnapOff guy, but I'm not spending that kind of money.
Time to go burn some gas!
Dan

 

Wot throttle chop.


Makes me concerned about the integrity of my head gaskets with the green tinge