ClassicCar

I have a 1947 Chris Craft with a Chrysler flathead 6 in it. Here's my problem. The engine starts very well and runs smoothly with new plugs in it but the plugs foul after a very short time - usually less than 1 hour of running. We figured the problem was the fuel/air mixture being to rich. The engine is equiped with a Zenith updraft carb that has both a low speed (idle) and high speed adjustment. We have turned the low speed screw in as far as it it will go (it still starts easily and idles well enough) and have turned the high speed adjustment (a t-handle on the side of the carb) in all the way and then back out one full turn. This seems to be a lean as we can go and still get smooth acceleration. Even with these changes, the plugs continue to foul in less than an hour. The fouling by the way is black carbon deposits on all 6 cycliners, although I have noticed that the plugs at the "bottom" (the egine is at ~10 degree slope to allow for a direct connection to the propellar shaft) of the engine seem to have more soot than the others. Seeing as this hasn't worked, my next thought is timing...what do you think? If yes, how do I advance or retard the timing? Thanks for your input. Randy