I have a 1976 Mercruiser 170 4cyl. I have been having the same problem for 3 years. I have had a tune up done, new ignition system, Compresson test and head casket checked. The engine runs great for every day use but every time we go fishing (idle for 3 to 4 hours) the boat will start to smell and push out yellow black smoke and kill.When it dies the lower exhaust unit expells black-brown oil into the lake. Then the boat will not start like it is flooded.The starter turns over slow but if I let it sit for 40 minutes or so I can get it to start but it runs bad intill it cleans itself out.Please help!!
