I have a mid 80's mercruiser 140. The engine free revs fine and idles ok, but under load backfires out the carb. This only happens running in the forward direction. In reverse this doesn't happen. We have trouble-shot the entire ignition system one piece at a time and this is still occurring. Both fuel filters have been replaced with new units and the carb has been disassembled and cleaned and appears to be functioning correctly. The fuel in the tank is new. The timing is set to 6* BTC at idle. There also seems to be a lot of "blow by" coming out of the PCV valve. What items should we be looking at to trouble shoot this problem?
