'84 mariner 75hp rough run untill almost WOT

[brad86]

I just bought an 84 sea nymph fish n ski w/75 mariner bout 2n a half months ago. Great boat great motor! Now it ran great until just a few weeks ago... The carbs looked a tad dirty(surface dirt) the previous owner said to run some sea foam in the tank...I tried it and ever since then it seemed to run kinda rough and felt some vibration during slow to mid throttle. Seemed to idle perfect though. Anyway it would do this until almost WOT. Then the whole rest of the time the motor runs great! Besides occasionly shifting from neutral to forward or reverse it will stall. That don't bother me really as I just give it a bit more throttle although it shouldn't die. Now I've replaced the plugs... Old plugs still looked good. Replaced fuel filter. I'm gonna stop using the sea foam and see what she does. This is not a huge deal to me however we all want our boats running top notch! Please help.

 

[Texasmark]

Re: '84 mariner 75hp rough run untill almost WOT

Give the SF time to do it's job. Matter of fact, you might up the ante to 2 or 3 oz per gallon or so till it clears out. Or you could dismantle your carbs and clean them, not a bad idea, and reset your carb/timing linkage per the manual. I learned of it on here back in 2005 and have been using it ever since. I recently tore down my carbs having been on the engine since '02 without being cleaned, and they were spotless inside, give a few pieces of black fuel hose that had gotten lodged in the carbs. But I should have replaced the line at 10 years anyway.

Mark

 

[brad86]

Re: '84 mariner 75hp rough run untill almost WOT

OK I have used SF in the last two tanks...shouldn't that have cleared it by now? My uncle whose a boat fanatic said to use stabill for now cuz seafoam is for later in the season idk. Everything else he told me has worked but I think I may go with cleaning the carbs out, checking fuel pump, and syncing. I just ordered a manual for it so I'll wait for that to show first. This is my first boat and I'm not too familiar with marine engines however I am with regular car engines. Don't know how much they differ from one another but I'll learn. Thanks mark.

 

[Dave1027]

Re: '84 mariner 75hp rough run untill almost WOT

I would not put seafoam in the tank. Just my opinion but seafoam is good for soaking the crankcase to remove oil build up but not good for mixing with the gas. Mercury sells their own version of sefoam called PowerTune. Their instructions do not say to add it to the gas.