I have a Rochester Quadrajet on my boat and have been attempting to tune it. It seems that I'm getting too much fuel in with my mixture as I'm blowing black smoke. If I close the mixture screws entirely, the black smoke disappears (although I see some very faint smoke), but even 1 turn out the black smoke returns.
As I understand it, these carbs should be anywhere from 3 - 5 turns out from bottomed as a typical mixture. I can't seem to do even 1 turn without creating a rich condition.
The carb is newly installed and rebuilt by a company rebuilds them and sells to the public.
Now, as a backstory, I was having issues with boat starting prior to what I mentioned above. I removed the spark plugs to find that they were covered in black carbon (I had recently replaced all of these 2 weeks prior but have had a series of various issues since that involved me changing mixture, timing having backfires, etc. that must have lead to the fouling of the plugs). I replaced all the plugs yet again and the engine started first try.
Now, after my above mentioned tuning attempt, I checked one of my brand new spark plugs I installed last night and it too has black carbon on it after just < 10 minutes of running since purchasing. That said, the plugs still fire fine.
So, I'm not sure if I'm just burning off fuel / carbon from my prior issues still or if this is due to the carburetor somehow dumping too much fuel into the intake despite the fact that I've closed the idle mixture screws.
Additional question: Where is the fuel coming from if the mixture screws are closed entirely? I checked all 4 barrels and I do not see any fuel coming from the jets. As far as I know, this only leaves the mixture screws as a potential source of fuel.