Your condensation problem is more than likely due to not driving it much or the PO not driving it much. I would say that your carburetor has little to do with the excessive condensation; an overly rich fuel mixture will cause poor idle, poor MPG's and fouled spark plugs. How often and how long is this engine run on a weekly basis, both now and previous? Look at it this way...Bran new engine...spotless...run occasionally never getting up to operating temps for very long, then shut off and let sit for a week or so. Now the moisture that has collected in the valve covers causes corrosion on the very clean new fresh valve train. You see because this is a somewhat fresh overhaul the metal is still very clean and has not had very much time to allow the oil to create the thin protective film that most engines have due to running for long periods of time at there ideal operating temps. As you use the engine the oil will start to from a very thin protective film over components, this is what keeps cylinders, valve train, rings, crank and so on from rusting when an engine sits. Do you think your engine is completely protected form moisture as it sits the engine bay waiting for you fire it up? Good quality oil, frequent oil changes and using your engine, not abusing, will prevent this from happening, if you do not use the engine very much add an oil additive which will help prevent his from happening. Some good additives are Marvel Mystery Oil and Lucas.
I hope this helps some,
Corey
