We have a 1984 Johnson GT 150. This week while fishing, the engine made a different sound maybe a miss, the next morning, it started, put in nuteral, engine died, would not start again. Engine backfires when trying to start. 2 mechanics said carbs w/junk. Cleaned the carbs w/cleaner, didn't help, changed plugs, wont start, checked compression, all had 85 lbs, removed carbs, cleaned all 6, no start. If this was an auto engine, I would say it has jumped time. Engine is firing. Sounds like it's firing too quick. Mechanics say it couldn't jump time. This engine was built at the end of 1983 and is a cross between an '83 and '84. Anyone have any ideas? Need help.