I have a 77 460 in a 77 F150. No modifications besides Hedman headers, Flowmaster exhaust, Edelbrock 1406 carb, and Ford Racing plug wires that are a mile too long. I'm running Autolite APP25 platinum plugs. I've been struggling to tune my carb's idle mixture, but it's tuned well in all other aspects. I'm having serious soot buildup on spark plugs nearest the front of my engine, especially those on the driver's side. The rear most plugs aren't even a golden brown color (like they should be). They're bright white and look brand new. The rear most on the passenger side are also white, but not as bad.

Any idea what could be causing this? It should be noted i do not make short trips anywhere. It's very frustrating since I'm trying to make this my reliable backup pickup once again.

 

Oxygenated gas doesn't show the same tan color as the full hydrocarbon gasoline of days gone by.
Plus the "nitrogen scouring agents" and other additives of some brands...

You need an illuminated loupe to see the ring way down (up?) at the base of the porcelain.
Ideally you would weld a test bung into the header and check with a wideband O2 meter.

If your plugs look sooty (fluffy) then you're too rich.
If the deposits are merely black, you might try going to a hotter plug.

I'm not one for fancy plugs or wires, so I really can't speak about that.

 

1 reply after 2 days??? Wow, this forum has gone downhill big time.

 

How does it run/perform?

 

I havent heard anything good about platnum plugs in these dinosaurs... I run the autolight coppers with no issue

 

you are running to lean,richen up the mixture till u get them tan

 

Are you crazy? -edited for content MB-

 

Insults are not necessary in here.

 

Neither are helpful replies, apparently.

 

It sounds like you are getting a wide variation in air-fuel mixture between the front and rear of the engine. This could be due to a vacuum leak - some vacuum ports connect in at the back of the engine/intake manifold (at least on the stock manifolds, not sure what you have on there now).

The vacuum leak could be causing a lean mixture for the rear cylinders.

Just one possibility.

I second the idea of using an O2 sensor and gauge. They are so inexpensive these days that there is no reason not to have one with a carburated engine. It eliminates a lot of guesswork.

If you have access to a secondary high voltage tester or oscilloscope, you can infer the fuel mixture by the firing voltage - the leaner the mixture, the higher the firing voltage necessary to fire the plug.

The base firing voltage depends upon the length of the wire (resistance) and the plug gap. I would guesstimate that your idle kV readings would be between 6 and 10kV (and all eight cylinders should be within a few kV of each other). If you have a lean cylinder, you may see 15-25kV. You can choke off the carb and watch the kV readings change.

I have a clamp-on kV tester that I bought for under $100 that is one of the most useful diagnostic tools I have in my box. I use it on everything from my cars to my lawn mowers and chain saws.

Good luck!