Petcock, Carb, Running Rich

[DCheney]

I have a 1967 CA77 Dream 305. I have left the petcock on, over night, on two different occasions. Both times, the next day when I run the bike, after a few min, it starts running rich, loosing power, bogs, and runs slow and jumpy. I just want to understand what is happening from someone who understands the bike. to fix, I had to drain the oil, and replace, if has a ton of fuel in it, and clean up the plugs, they are VERY black). Can anyone tell me what is happening when the petcock is forgotten on?

Thank you in advance,
David

[garncarz]

Without looking at the bike, this is just a guess: The carb float is set too high and somehow the overflow is blocked allowing fuel to flow via gravity into the carb and then down into the cylinders. It then leaks past the rings into crankcase. Hence, fuel in the oil and a rich condition.

Take the carb apart, cleanout all the passages and the overflow and reset the float to 26.5 mm; measured from the carb body (gasket recess).


Once again, just a guess. Anyone else want to chime in?