"New" 15hp 2010 Mercury intermittently runs great, then the next second, rough.

[cricketchaser]

[FONT=&quot]Hi guys. I just purchased a 2010 Mercury (Tohatsu) 15hp 4stroke. It appeared to be rarely used as there were no scratches on the prop/foot. It ran great on muffs at the previous owner's house. Today, I took it out for the first time. Initially, it cranked great and idle smoothly. I let it warm up for about five minutes, and proceeded to slowly open the engine up. It was accelerating smoothly until it got close to WOT when the RPMs dropped and the engine started running rough. After that, the engine would intermittently idle and run under part throttle fine, then the next second, go back to rough with reduced RPMs. It would try to accelerate, and sounded fine, until it got to half throttle or se. Then, it would start coughing and generally being unhappy with life - going back in forth from running great to running rough.I pulled each plug wire, and each time the engine died. I used a fuel tank I already had with fresh gas. Any ideas?[/FONT]

 

[cricketchaser]

Anyone?

 

[RickM46]

Since it was used infrequently, maybe carbs are gummed up? Maybe new plugs? Run some seafoam thru it? Clean the carb? Check output of stator but since it was not used much, maybe spark is OK? Did a search for Tohatsu service manuals and found this: https://www.downloadboatmanuals.com/motors/tohatsu/ to get specs.

 

[InTuneMarine]

Did you find the cause of the problem? I am having a similar issue. Runs great for 5-10 min full throttle then loss of RPM and runs poorly. Primer bulb hard, it acts like its overheating or losing spark but the tell tale has good pressure.