318 rough idle dies when put in gear

"Here are the particulars, new

"Here are the particulars, new long block (20 hours), new Carter AFB carburetor, new Mallory electronic ignition and spark plug wires. Old exhaust system which I fear has caused serious problems. The boat ran fine the last couple of weeks but has recently started to idle rough. There is a hose coming from the bottom of the carburetor that leads to the pcv valve that pulses on and off with vacuum pressure causing the pcv valve to click. The engine feels like it is missing on a cylinder. I pulled the valve covers and noticed a little bit of white sludge. I know this indicates water intrusion but there wasn't a significant amount of sludge so I'm hoping it was just condensation. I fear a valve is stuck open, but am hoping there is another, cheaper explanation. With the valve covers off the rocker movement seems fine. Is there an explanation to my problem that I may be missing?"

"Warm the motor thoroughly and

"Warm the motor thoroughly and set the idle speed at 1,500 rpms. Using insulated gloves and pliers, pull each ignition wire out of the cap, one at a time, then reinsert. Note the loss of (or not) of idle speed as you do this. If a cylinder doesn't respond, note it's location. Then pull that plug and note its color. If dark, change the wire AND the plug. I suspect this is the problem.

Another thought... Is it possible your carb is merely flooding? You can tell by turning the idle mixture screws in 'til they bottom out. If the motor stays running, or picks up speed, the carb is flooding.

A certain amount of condensation is normal IF the motor hasn't been run hard for a while. But keep your eye on the oil color.

Jeff"