I have a 1982 Mercruiser 140. It has been running great all season. Recently it has started to run very rough and even stall after it has been running for 20-30 minutes. I have a Mallory distributory that is a year old. I set the dwell at 34 and the timing at 6 BTDC. When the engine is running rough, the dwell jumps to 60. There is no play in the distributor, but if I push on the cap I can bring the dwell down and increase performance. The screw on the points seems tight, and nothing has visibly changed, but if I loosen the points and reset them the problem is temporarily resolved. I cannot imagine a problem with the points, condenser, or cam that would cause this problem. Any thoughts?
