I have a 67 F100, with 92,400 original miles - 352V8, Autolite 2100 original (rebuilt) carb. I was doing a minor tune up and found that the plug in cylinder 4 was more carboned up than the rest. I was wondering if there is something I should be looking for that might cause this. These plugs have about 1300 miles on them over the last 3 years. The engine runs well, and doesn’t seem to burn oil between changes. I will rotate the plug from cylinder 4 to another cylinder and will check it in a couple of hundred miles to see if it may be the plug.

-Spark plugs (Motorcraft BSF42CA) and cylinder compression are indicated in photo. Compression test with all plugs out, WOT and choke open.

-Initial timing set at 12 degrees at 560RPM with vacuum advance disconnected and plugged.

-Manifold vacuum at 550 RPM – 19 inches. Throttle snap down to 5 inches, up to 25 inches and back to 19 inches.

-Gas mileage on out of town roads (50-55 mph) is 15.6 mpg (imperial gallons) which I think would be around 13 mpg (US gallons).

I am not a mechanic and have not worked on engines since I was a kid in the 60’s so I’m just going on what I read about tuning these old engines. Any thoughts would be appreciated.

 

Other 7 OK. Hard to see from here, but if ...

Just #4 Shiney Black, wet oily looking deposits ... oil fouled. Valve stem seal likely worn out / cracked.

Just #4 Dry Black sooty deposits ... fuel fouled from simply not firing. Plug bad likely ... or plug wire / cap..

Not timing or carburetion ... as other 7 are OK.

 

What I have is "Dry Black sooty deposits ... fuel fouled from simply not firing. Plug bad likely... or plug wire / cap.."

Thank you tbear. I will start by rotating/ or replacing the plug, and if that doesn't solve it I will move on to the wires and caps. A new set of wires is probably not a bad idea anyway.

Any suggestions on type and quality of wires. This is a stock engine.

 

Factory Motorcraft wires are still available from a quick glance in the old interweb.

 

I am sure Motorcraft would be ok , but silicone , spiral wound 8 or 8,5 mm are the rage , .........
I sucummed to the slick marketing reviews & got Accel wires that look great ,
I spung for a set marked way down on sale , I wanted red but settled for brite yellow with a black stripe...........