Black spark plugs

[Wedgetail]

I put in new spark plugs recently (1940 Deluxe), and within 10 miles they were all black and sooty. Presumably the engine is running rich. I rebuilt the carburetor, and found that it looked like it had been rebuilt recently and all the gaskets looked new, just like the new ones I bought. If I pump the throttle with the engine off, a little gas leaks out of the throttle plate axle (no seal there). If I clean off a spark plug, it gets black and sooty in a couple of minutes. Is this a problem? What else can I do?

 

[SoCalCoupe]

Spark plug reading is tricky. "it gets black and sooty in a couple of minutes." If that means the engine is cold and just idling, it doesn't mean anything. Or even just idling, may not mean much.

 

[petehoovie]

 

[TerryOH]

If your driving your car and find the plugs to be covered with soot as #7 above photo or even worse. The problem is most likely the Carb. or it's adjustment. The 40 Ford has a Ford or Holley 94 Carb model 91-99. Before disassembly adjust the idle mixture needles for the highest vacuum and smoothest idle and see how the car and plugs respond. If you disassemble it should have .050" main jets. It is possible the fuel level is too high, or the power valve or it's gasket are leaking. Daytona is about the only place to get a rebuild kit with the proper replacement parts but I would still keep the inlet valve and it's steel needle.

 

[rustedorrotting]

If it had been rebuilt lately, the problem is most likely the power valve. The ones available today have a radius next to where the seal sets which wont allow it to seal. pull the carb and the valve and look at the sealing surface. www.charliesspeed.com buys these valves in bulk and machines the radius off. If I can be of any more help, let me know. I have recently been rebuilding/restorring these old carbs.