91 Merc v135 still acting up

[BRIELLY]

I thought I had solved my problems but after a long trip and breaking down I guess not. So far Ive rebuilt the carbs, fuel pump and installed a new rectifier and checked all fuel lines, filters and tank. Ive squeezed the bulb while its almost dying but that doesn't seem to do anything. The problem only arises after running for at least a 1/2. It will run flawlessly at 30 mph but when I back off the throttle it sputters at slower speeds. After shutting down it will barely idle and just dies if I try to give it gas. I'm assuming this is some type of iginition problem since I imagine if it was fuel the problem would be more consistent??? Unfortunately it looks like I will have to break down again to duplicate and check the problem. I'm planning to bring my spark tester and an extra coil hoping that its just a bad coil. Is there anything else i should check while this is happening? I'm also wondering if the oiling system could cause this problem after running for a while. Ive noticed some oil lying in the bottom of the cowl and it is a bit smokey at startup but not too bad once running. I guess I'll pull the plugs and see if they are fouled. If anyone can give me any suggestions on what to test or look for when this happens i'd appreciate it.