2000 Johnson J115JPLSIF 115/80 Jet

by Chas
(MT. CARMEL PA)

Ok, here is the problem..A few weeks back, while running the boat on the river, My motor started sputtering while running on plane. Basically it would be running fine, then all of a sudden it would bog down or sputter, but then it would clear and run fine. I took the boat home, changed the plugs, cleaned the screen at fuel intake, which was clean anyway, and for added measure installed a fuel/water seperator. I also checked fuel lines for breakdown of interior wall but all was fine.. I took the boat out again this weekend and sure enough it would spit and sputter intermittently while on plane, but here is the perplexing kicker...The boat runs perfectly fine upriver with no sputtering, it 100% only does it going down river... to prove my point, I took 3 friends at 3 different times to show this to them and all 3 times, the boat ran perfectly fine upriver, but it would act up going down...Help!!! Now before you say its cavitating,it isn't, The rpm's dont over rev, and the sound just isnt the same as cavitation, which Im aware of, this is like I said more like a bog down miss or should I say a hiccup..also, I have this boat and motor since new, and never had probles with it, I faithfully run starsan and stabil marine in it and faithfully change the plugs every 2 years..can someone please point me in the right direction ? Thanks