1999 3cyl Mercury Force Missing? 70?

Question

Got a 99 Mercury force 3cyl. 70hp (I think if not its a 90) anyway. The middle cylinder is missing, but if I pull the plug out its got spark. I took it back to the shop that put the motor on. He played with the wires removed the plug and magically it was running fine, never gave me a real reason for it. A couple weeks later the middle cyl is missing again. Still got spark, dude tried to tell me that sometimes the carb to save gas would not send fuel to the middle cyl... I dunno, its got spark when I remove the plug...??

Answer 1

this engine was Mercury's first attempt at fuel consumption reduction.  The engine isn't in production anymore because of the problem you are listing here.  I don't know how to help you but my personal experience with the motor if you run it hard for about 10 min the third or middle cylinder seems to open up.

Answer 2

Mark G has it right.  As for the middle carb thing, it is not true.  However on older Mercury inline 6 outboards at idle the top 2 cylinders did not run, but once given throttle they kick in.

Answer 3

The carb thing is bogus, period. I've been around this stuff my whole life and I've never heard of that, nor would I ever think of telling someone that. Either way, you might just need a new set of plugs. At our marina, unless the owners' specify otherwise we put new plugs in all of the 2 cycle outboards w/ the exception of the new (2000 and up) OptiMax's, HPDI's, and FICHT models. That just gives both the boat owners and us peace of mind for the summer season. Make sure your carbs are clean...the build up will foul plugs and can burn up your motor if they're dirty. Also, you'll want to make sure it isn't running too rich. The only other thing I would check would be your plug wires and your coils...but I'm betting on the plugs. Good Luck!