Mercury 9.9 running rough mid throttle

[doc2b4fun]

Hello all.. Im hoping someone may have some words of wisdom for me. I have a 2014 Merc 9.9 4 stroke on my hunter 23.5. It has always run great without problems. I have done the usual maintenance and put a new water pump last year. At the end of last season the engine started running really rough, kind of stuttering and then sometimes revving back up in mid throttle. it never stalls. it seems to run ok at idle and in "gear" or at low throttle as well as at high/full throttle. the problem only seems to occur when in the mid range of the throttle. I just fired it up with earmuffs on and i still have the same problem. its only 5 years old with maybe about 75-100 hrs on it. I took the carburetor out thinking maybe it was gunked up but it did not seem to have obvious buildup to the naked eye. I cleaned with carb cleaner all the valves, the needle the bowl etc and put it back in hoping that would solve the problem but it did not. before i did this i flushed out the fuel lines to make sure it was all fresh gas in the lines but no change in this problem. i put new sparks in as well. The fuel filter does not seem to have any junk in it as far as i can see. Where do i go from here??
thanks in advance for any advice.

 

[jibes138]

Sure sounds like a fuel delivery issue, possibly the fuel pump? Try this make sure you mount your squeeze bulb in the fuel line in a vertical orientation with the fuel flow direction facing up. Also get a new one while your at it unless your fuel line is new anyway. Also get a fuel filter/water separator if you don't already have one and mount it on the boat so your fuel line goes to that then to the squeeze bulb then to the engine. I have also heard people having good luck with ultrasonically cleaning their carburetors to make sure all the internal passages and orifices are clean. You can buy a cheap bench top unit for this or take it to a shop and ask them to ultrasonically clean it. Run it dry before storage by disconnecting the fuel line and letting it stall. Have you tried squeezing the bulb while it is running poorly to see if the sudden surge in fuel improves it?

 

[rgranger]

Sure sounds like a fuel delivery issue, possibly the fuel pump?

Revving up usually means it is starved for fuel. I'd try buying a new line... and/or check the pump. And like @jibes138 said... I always disconnect the fuel line with the engine running when I get to the dock and let the engine stall.