I have a 70 hp Johnson outboard motor (1987). It starts fine and idles fine, but when I open the throttle it dies on me. It does not run ofer 1000 rpm in the water. It seems like I am getting air in the system. Could there be a problem with the tank or the lines ?

I also have a 1987 - 70 HP johnson. I have a similar problem. It starts and idles. I can go slowly up the lake. When I hit the throttle it dies. Also, when I am under appx 1/3 throttle, going slowly up the lake, it dies, starts up and goes a while longer and dies. I have changed the lines, the gas filter, the pump. I have a friend who told me it might be an ignition problem. Did you find out what it was? Does anyone have any idea?

Clean the carbs

I had the same problem on my 1983 70 hp evinrude. After cleaning the carbs,rebuilding the fuel pump, and looking for air leaks or blockage I decided to do a compression test. The top cylinder had water in it. Removal of the cylinder head found the head gasket blown.
After replacement of head gasket the engine runs better than it has in years. Check your sparkplugs, they should be a golden color and not look brand new. Water in the cylinder tends to clean all the carbon deposits off the sparkplug. Good luck

Does any body know the torque sequence for a 1980 70 hp johnson. I also had the same problem blown head gasket. If you do I would greatly appreciate the info