please help 04 115 2stroke fouling 1 plug

hi i'm new here and i need help please . just bought an 04 nitro 750 with a 115 2 stroke carbeurated engine. while at the marina picking it up the guy tried starting it without the kill switch on for about 20-30 seconds. he got it started and it sounded fine but when i took it out for the first time it was idling rough and hesitating to take off it seemed ok at full speed mabye because not enough load on engine. pulled plugs and the third down from the top was black and wet the others were fine. repalced all 4 took her back out and it was better at first but still not quite right and as the day went on it got worse. pulled plugs when i got home and the same plug was very black but not wet. kind of sutty. what could it be and is there anything i can check
myself before taking it to a dealer and spending lots of $. thanks

Re: please help 04 115 2stroke fouling 1 plug

I would guess you either have a flooding carburetor, or a fuel pump problem. The fuel pump operates off of vacuum and pressure pulses from one of the cylinders. It is possible it is #3 on your motor. If the pump is leaking back into the cylinder, you will get the problem you are indicating. If you remove the screws holding the fuel pump to the block, squeeze the primer ball, gently and see if fuel leaks from the hole in the back side. If fuel does leak out, then your fuel pump needs rebuilding or replacing.