200hp Carb'd. Merc - Sputtering and stalling

[Mullady76]

Guys,
I had some problems with my engine yesterday.   I would start the engine and it would idle fine, then when I throttled up it would start to sputter, loose power, then stall out.  To get it re-started I had to crank it for awhile with the throttle wide open.  It would stumble once or twice then restart with a big cloud of smoke. This happen every 3rd or 4th time I tried staring it.   The engine ran great at 3k rpms and up, but I now notice a slight cough at idle and low rpms.  It also seems to be struggling to get the boat up on a plane.  Once I hit 3K, it takes off like a rocket.  The engine has a new stator, plugs, and new fuel system with fresh premix.

I do have to play with the neutral safety switch sometimes, but I don't think that is part of the problem because motor is turning over.  Does this sound more like an electrical problem or fuel related? 

Thanks, Sean

[love2fish]

sounds like a simple carb job will work. probably some of the jets are clogged and/or the floats are catching given the works/doesn't work at different RPM's.

pull the carbs and clean em.

[fitz73222]

What year is this engine? Post the serial number. Several things come to mind. If the engine is running fine at high speed but loading up at idle could be a leaking fuel pump diaphragm or sticking check valve in the pump that is dumping excess fuel back through the pulse line into the crankcase, a defective idle stabilizer box, another bad stator if it is the old two stage design. if you are running E10 fuel on a constant basis, the whole fuel system is suspect for contamination, degrade and pieces of fuel line debris stuck in the carbs. When's the last time you replaced the fuel filters assuming you have a water separating filter in the boat and the engine mounted filter under the cowl that most people forget about?

[Mullady76]

The motor is a 98 with unknown hours.  Serial # 0G591450.  Its the older design with the (2) power packs.  Fuel lines are 2 years old, fuel pump was rebuild last season, and all new fuel filters this season with about 15 hours on then.  Yes the fuel is E10, that's all we can get up here.  Its always purchased from a high volume gas station, premixed 50:1, stabilized, and ring free added.

It idles fine, but has that slight miss or cough.  It sputtered and dies only when I throttle it up.