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427 Troubleshooting: Fouled Plugs

December 3 2006 at 11:40 PM
William Mulvey  (no login)

Some troubleshooting to ponder during winter layup. Challenger was hauled and winterized this week but a problem with plug fouling reared its head in the post season. If you can see in the attached pic, some were carbon fouled, giving me some obvious conditions for rough running. Extended idling time is unavoidable with a slow speed limit in the channel back to the marina.

Some background . . . virtually untouched engines since factory fresh in 1973 and each have giving 2100 hours of great performance. All maintenance done at the same marina by the same master mechanic since the boat was delivered there. Oil has been changed every season and neither engine has ever required additional oil to maintain level on the dip sticks. Valves were last adjusted perhaps 20 years ago, but no one is sure. Fuel is 92 octane with lead additive. Carbs and distributors were re-built 10 years ago. Both engines have always been great starters.

Paying close attention to the discussions here, we did the following upgrades late this season.

1. Upgraded to Splitfire ignition wires. This offers lower resistance than old 1970's wires. For example, the old coil wires metered at 11,480 ohms while the new Splitfire coil
wire is 370 ohms. All wires were carefully loomed and routed to prevent crossfire.

2. New Champion RF10C plugs gapped at owner's manual specs. Points, rotors and new caps along with timing.

3. Timing light confirmed fire at each plug.

At this point, plugs were still fouling with dry black soot... not on all plugs but generally about the front four on each engine. Running at 920 rpm in the channel back to the marina always seemed to add to the plug fouling situation.

Next steps.

1. Marina owner agreed to check the valves. After all these years, they were all consistently at .025 cold and .021 hot.

2. Compression test . . . all within factory specs, hot AND cold, 160 - 190 lbs. I'm presuming that this is a good test of the valves and the cylinders.

3. Installed Pertronix electronic ignition.

We were at a freeze risk last week so the boat had to be hauled. We couldn't test the new ignition out on the lake.

Mechanic's recommendation is to re-build both carbs as he found one dead accelerator pump on the port engine's carb and he's suspicious of the automatic chokes. This will be done over the winter. He has always leaned the mixture as much as he can to avoid running rich.

Though I requested a valve job if necessary, he doesn't feel that it's necessary at this point.

If you can think of any other winter projects that could improve Challenger's performance next April, any ideas would be appreciated!

As always, thanks guys, for contributing so much to the Commander community!

1973 ChrisCraft flushdeck Commander 41

PHOTO OF THE DAY AWARD (December 5, 2006)

"The photo above showing off the motor block and spark plug wire insallation was featured as the "Photo of the Day" on December 5, based upon it's composition, clarity, color, and relevance to the discussion at hand. Nice job, Bill!

forum moderator

Reference comment added, the link below is from Professor Toth's Plug Wire 101 class (there will be a pop quiz in the morning):

This message has been edited by FEfinaticP on Dec 8, 2006 7:48 AM

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(no login)

Hello Bill, good hearing from you

December 4 2006, 12:39 AM 

Hope all is well with you and yours.

You say the compression is strong, so that's a fair test of rings and valves.

Right off the bat I'd go after the carbs. I suspect a rich running carb with the automatic chokes being the culprit. My chokes have been wired open, I never use the chokes for starting, as I'm one of those throttle pumpers. I pump as many times as I think I need, some times more if the boat hasn't been run for a couple weeks, you get the idea. I don't like the idea of a 40-year old "automatic" device causing a rich running condition.

Under running conditions have you noticed a gas fume smell (unburned gas), which would be from an overly rich running motor? This would be especially noticed at the dock under idle conditions. If it's not the carb then it's oil that's being burned, which is not necessarily a bad thing. As engines wear, the pistons, rings, and cylinder bores all wear a little and more oil is admitted to the combustion chamber.

In addition, you can get oil dripping slowly down the valve stems too, and this may be corrected with valve stem oil control seals. If you have a high milage motor, you can adjust the plug to burn a little hotter to compensate for this too. A change of oil type and spec may help some too. If it is oil you're burning to cause that soot, you should be seeing some degree of blue smoke on the water. If it is valve stem seepage, I would think you'll see some blue smoke upon startup too. If it's oil that's causing the soot, and it seems to get worse while running around 1000 rpm, then you should be seeing some degree of smoke.

If it's a rich carb, you probably won't see much of anything but you'll smell it if you back into the slip and stand behind the boat.

I think your trusted marina mechanic was on target when he said you didn't need a valve job. You may need some valve stem seals, and it is possible to install those without pulling the head, but it's a hat trick to do it ( you have to be careful not to allow the valve to drop into the cylinder, or then you will have to remove the head. People have been known to stuff closeline into the clinder to act as a buffer.

You have great wires now, the plugs are right, be sure you are using the ballast resistor as required by Pertronix (see the Master Index 427 section on PERTRONIX if you haven't already seen the diagram). If you are sooting over while running around 1000 RPM, I think its the carb, but as with these old boat motors, it could well be a combination of two or three things working together. I'm an optimist!

I'd be interested in hearing some of the other guys chime in on this one, so gentlemen, please fire away when you are ready!

Regards, Paul

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Bill M
(Login NYBill)

Over rich carbs

December 4 2006, 7:11 PM 

Thanks again, guys, for all the on-line diagnosis. The consensus seems to lead to carb issues, so hopefully this winter's rebuilds will cure the problem.

Here are a few answers to the questions brought up in the threads:

1. No blue smoke has been seen and I've looked for it. Also, no gas smell has been noticeable. Exhaust water does occasionally have a slight floating rainbow, but then I've never seen a marina basin without it. Also, NO oil consumption.

2. The only noticeable symptom in addition to the black soot on the plugs has been a blast of soot fired out the exhaust if I've changed spark plugs. That stuff floats!

3. Based on prevous posts regarding those automatic chokes, I agree that it's unlikely they're working right after 33 years. Time for them to go away.

And a question to Jerry . . . if those valve guide seals have actually ridden up on the valve stem, would the mecahnic have noticed that, or are they still out of sight with the valve covers off?

Thanks again, guys . . . I will follow through with a report in a few short months when the boat can float again in an ice-free Seneca Lake. All of the advice and suggestions are awesome and appreciated.
Bill M
1973 CC Commander

PS: I hope Tim Toth sees my pic of my new iginition wiring . . . it's a challenge matching his craftsmanship.

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Tim T
(no login)

Re: Over rich carbs

December 4 2006, 10:43 PM 

Good looking detail job on your plug wires !
I knew you would "see" the performance increase with an ohm-meter .Make sure you do not have an air leak on the choke heat pipe where it attaches to the exhaust manifold and the choke adjustment knob .
Your engines are fine ,just re-build the carbs during the off-season ,replace the plugs with a " projected nose" style plug,Champion -RF9yc or Splitfire - SF4E .,set timing to 10.5 with a digital dial-back light and you will be set .
Tim T
Sandusky ,Oh

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(no login)

Valve stem seals

December 5 2006, 6:32 AM 

Bill, your mechanic would probably not have seen them. I doubt if he even looked under the valve covers. Even if he did, he might have missed the backside of one that was broken. When these go out, you generally know by looking in the rear view mirror, because you are smoking down the neighborhood.


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(no login)

Two types of seals

December 5 2006, 7:04 AM 

Later seals were a nylon type, that would handle heat and oil better. The early seals were a Viton soft rubber.


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(no login)

Valve seals can be changed without pulling the head

December 4 2006, 12:48 AM 

Ford used an umbrella type valve guide seal, and they have been known to ride up onthe valve stem. They get brittle with exposure to heat and hours, and they can break off. I have heard about the rope trick, but using compressed air works better. This operation can be done while the heads are still on the motor.


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(no login)

Ford 427 valve seal info

December 4 2006, 2:30 AM 

Hi Bill,

Since the valve seal topic came up, I decided to start a dedicated thread to that particular issue and it can be found here (for your reading and photo viewing enjoyment !)

Regards, Paul

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Tom Slayton
(no login)

Over rich carb ?

December 4 2006, 10:52 AM 

This is the classic image of a carbon fouled plug due to over rich carb.


Here's more

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(no login)


December 4 2006, 10:57 AM 

Almost certainly the carb if it's primarily idle/slow speed related.
Adjust the idle air screws for max rpm at idle. Even after a rebuild, mine run best at 1 turn out. A new carb is usually 2 1/2 turns, and that's the way most mechanics will set them.
Over the years, you can get air leaks at the butterfly shaft seals. This will also cause a rich condition. If that's the problem, it's time for a new carb.

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Mike Frazier
(Login mfrazier)

Fouled Plugs in 427s

December 4 2006, 2:05 PM 

Regarding those fouled plugs, I also had the same problem in both my 427s. Originally, I thought I may have too much lead additive in my tanks. I remember that caused my brother's '63 Fairlane to foul plugs for awhile. After running last summer without any lead additive, I still fouled plugs.

Just a couple of months ago, and for totally separate reasons, I checked the timing on both engines. Both were off the mark. After making proper adjustments, I seemed to have accidentally fixed the fouling plugs problem in both engines. As already stated, many things can cause plugs to foul, but in my case, setting the timing per the spec seems to have fixed my problem.

Mike Frazier

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(no login)

Carter tuning tip (rich mix at idle)

December 5 2006, 10:14 AM 

If you see any "liquid" at all in the carb as it is idling, you have a rich condition and need a rebuild. At idle a carb should be running on fumes, alone, and NO liquid at all. If you see even a drop coming from the location around the step-up piston and rod cover plates, your motor won't be running well at idle and you'll probably smell a rich mix. I have one now that appears to be doing this, and I intend to pull it accordingly.

Regards, Paul

This message has been edited by FEfinaticP on Dec 5, 2006 10:29 AM

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(Login cadunkle)

Re: 427 Troubleshooting: Fouled Plugs

December 11 2006, 4:44 PM 

Firstly your spark plug sounds like a rather cold heat range. If you want to stick with a Champion plug I would recommend trying a RF11YC or a more likely a RF14YC. Those are the next two steps hotter in plugs that Champion makes. I ran some really cold plugs on a high compression Ford before to avoid preignition caused by spark plugs getting too hot. I ran the RF11YC and then moved to RF9YC. They fouled easily but let me run pump gas. Even when the car was stock I tried Champion RF18YC plugs (recommended heat range for teh motor) and they fouled more easily than other plugs I've used.

Since then I stick with Autolite spark plugs in my Ford motors. Personally if it were me I'd start with a set of trusty Autolite 45 and take it from there. Get the engines up to temperate and go for a short cruise (be sure to get on it a bit though) then pull a couple plugs and see what the heat range looks like.

You can tell if the heat range is too hot or cold by checking where the discoloration on the ground electrode stops. It should stop right about in the middle of the bend in the ground electrode. If it's more towards the  threads then you have a plug too hot for your motor, so go colder and try from there. If the discoloration stops before it gets to the bend in the ground electrode (more toward where the tip of the ground electrode is nearest the center electrode) then you need a hotter plug. Unfortunately since your plugs are so badly fouled I can't tell fomr looknig at them what the heat range is like. I will say that as far as Champion plugs go a RF10C sounds rather cold for a stockish FE, which can contribute to fouling.

Your plugs fouling are most likely from too rich a mixture. Air entering from worn throttle shafts is a possibility, as someone else mentioned. It will however NOT cause a rich condition. It will in fact lean the mixture as fuel is added to the air stream upwards of the throttle shaft bushings. You will typically get a lean idle and low RPM operation (doesn't affect high RPM nearly as much). Your idle speed may be arratic, sometimes slightly higher or lower depending on if your throttle shaft vacuum leak is erratic or if they are worn enough to leak constantly. If it is a very bad leak you may get a slight surging at idle and off-idle.

One easy thing to check to see if your carbs are giving you trouble in the source of a rich situation (despite adjustment) is to run the engines up to temperature and shut them off (do not pump throttle before shutting them off, just let them idle for a minute or so and shut them off). Then go look down each venturi at your throttle blades (use a flashlight). If any of the throttle blades look at all wet you have found the source of your over-rich problem. This type of problem is most often caused by boiling/hot fuel. Other typical causes include worn or dirty needle and seats, sunken floats, or things of that nature (basically anything that can cause an overly high fuel level in the bowls).

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(no login)

Thanks for the comments Cory

December 11 2006, 6:20 PM 

Any time someone takes the time to give someone else a hand, it's appreciated. Your info is of interest, especially as our boat motors get older and need some special care. The big Ford called for a F-10 Champion, and since those are no longer available, they've been cross referenced up and down the charts. Here is a thread from our archives. I would be interested in any follow up comments you may have. Depending on the age of the motor and the kind of boating being done, one plug or anther may be the best choice. Our boat motors don't normally turn over 4000 RPM and there are few people out there who run them at that speed (for very long, anyway) because they suck the gas and there's not really a need to race motor homes, if you know what I mean

Most of the time our boats are running between 1500 and 3000 RPM on an uphill grade. At 2600 RPM my 38 is up on a plane and feeling pretty efficient. A little more speed and she is equally happy. Based upon these comments, I'd be interested in any more plug observations you may have.

Regards, all the best!


I want to change the plugs on both engines after 3 years. What does everyone recommend. I took the spark plug numbers listed in the CC 427 manual to my local Auto Zone and got completely blank stares from them. Serves me right. They are not into 40 year old boat engines.



Autolite BTF-3 or Champion F-10 were what was specified for the 427. I am using the NGK A6FS, which I understand is a cross reference to the F-10, which was a pretty generic plug for Ford marine engines "back then".



I work at Autozone Part-time. Most of the other employees won't even try to find a comparable part if you say anything about a Boat. I am usually successful in finding most comparables, but I always give the disclaimer, on what should be marine. Some times I have to break out the Books in the store, to find comparables, most of the other employees don't know they exist. If its not in the computer, they think it doesn't exist.
I went to the Autozone website and put in the Numbers listed by Tom and they cross-referenced to:



DENSO 5014


I believe my store (Serverna Park Md) stocks these, and we are a low volume store. So most Autozones will stock them or be able to get them in 1-2 days. Just give them your existing spark plug number (or Toms listed number) and they can cross reference it.

The Eagles Nest


Excellent research and post, Rob. Taking your lead, I went to the Champion spark plug web site and I typed in the plugs you noted, and that Tom noted.

If you use this site, only type in the numbers, don't put in the name of the manufacturer, such as "Autolite" or "Delco" or any of that.

I ran a couple of the plugs you and Tom noted, and every time the Champion RF10C came up. Therefore this appears to be some good info! Thanks a bunch for the contribution, collaboration like this is great, and it will help a lot of people who have the same questions and needs later!

Regards, Paul

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Tom Carlson
(no login)

Anyone tried Platinum plugs?

January 2 2011, 12:10 PM 

Wondering if anyone has tried or has an argument for against platinum plugs for CC 427 motors?

It looks like an Autolite AP 124 is the appropriate size/temp range.

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(Login Gboom)

Good Question

January 2 2011, 6:43 PM 

Tom, good question.
Paul and all you 427 guru what is the best plug?
My engines will have a little more pop than the stock 427, which makes me a little more concerned.
I have not asked my builder for his opinion, but the forum is such a great source I look forward to the answers.


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(Premier Login FEfinaticP)

I don't have the (final) answer....

January 3 2011, 11:16 AM 

I use these 4-prong jobs in my 27 year old 928 P-car, at ten bucks each.

[linked image]

Not sure these are available for the 427 heat range or compression/fuel mix. Just going from regular to platinum, staying in the same heat range, would not do much except last longer? I have heard some bad things about Champion plugs, but I'm running those in my 427s now. There are probably better choices than Champion out there, but hey, they were made in Mexico so..........




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(no login)

Champion Plugs

January 3 2011, 4:46 PM 

Paul and all;

I've been told not to use Champion plugs in alum. heads, the threads are poorly made.


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(no login)

Use anti-seize compound in aluminum heads

January 4 2011, 9:35 AM 

I have heard, and have always used anti-seize in aluminum heads ever since I stripped one on a 1965 Alfa Romeo and had to have it helicoiled.


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(no login)


January 4 2011, 7:12 PM 

Paul and all,

Most deffently use anti-seize were alumium is involved, but if you look real close at the threads on a Champion plug, you will see a poorly rolled thread. Most cases you can feel the rough thread.
I have a stick of anti seize I carry in a tool kit on my HD just for plugs.
Don't even get me started on stainless steel.


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