Mercury 100 hp problem

[flasher]

I have a 1989 Mercury 100 hp 2+2 engine.The engine has a rough idle,sometimes it backfires.i originally thought that it was dirty carbs/fuel pump.I rebuilt the carbs,and fuel pump. i did the link/synch on the engine with negative results.I noticed that if i run the engine with one of the first two cylinders it runs smooth on that cylinder.if i put the spark plug wire in to the other it immediately starts to run rough.it does not matter witch one of the top two,it'll run fine as long as i dont connect the other spark plug wire to it.any help will be appreciated,thanks.

 

[flasher]

Re: Mercury 100 hp problem

well i though that it was an ignition problem but it appears that is not.it appears that the second carburetor has a fault.i tried to adjust it as per the manual 1 1/4 turns from a seated position,but i have to turn the mixture screw almost closed for any adjustment.the mixture screw has an effect on the idle from a seated position to 1/4 of a turn,after a 1/4 of a turn it does not affect the idle.i believe that its flooding.