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1988 Mercury 90 HP bogging down

J

Jaman_24

New member
Hey guys looking for a little help with my 90 hp mercury. It's a 1988 and I bought it last year. It ran fine the first time I had it out and then I took it to palisades reservoir and from the get go it would bog down and just wouldn't go. Initially I thought it was an elevation problem because I took it home and the same day took it out again at a lower elevation and it ran fine. I had it out lots last year and occasionally while on the water it would start to bog down again and then it would release and have full power. That's been the case for awhile now but it always releases eventually and runs fine. I thought maybe it was bad fuel or water in the fuel and that it would eventually work its way out with new fill ups. Well I had it out last week pulling the kids on a tube and I ran over a stick and thought it might be stuck between the transom and motor so I lifted the motor up. There was no stick so I dropped it back down and immediately it started bogging and would never release. Took it home and drained out all the fuel thinking maybe water was the problem. Put a bottle of star tron in it and filled it up with ethanol free premium which I always do and took it back out. Still bogging and just won't release like it normally does. The bubble is hard when running it. I tried opening the gas cap thinking maybe it was oxygen starved and nothing. Unplugged the fuel line twice and just let it burn out all the gas thinking maybe a float was stuck and still nothing. At this point I am stuck. Not sure what to do. My next step is to replace all the spark plugs which I did last year so I doubt its that. I'm not sure if this is an electrical problem or maybe carburetor problem. I hate to rebuild the carbs if that's not the issue. Anybody got any thought??
 
I'm looking on the parts manual and the only jet screw I see is the called the main fuel jet. It's located in the lower unit if the carburetor where the float sits. Is that the jet you are talking about?
 
No, not it.-------Main fuel jet is NOT adjustable.--------Look for a screw with a spring on it to keep it from moving by itself.
 
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Pretty much talking to myself here but anyway. I changed all my spark plugs today and took my boat out and it ran great. What the heck? Not sure if this is just a fluke or what but I'll keep running it and see what happens.
 
After a few trips pull plugs,check for excessive carbon ,oil fouling,plugs should be tan to light brown,Running lean is fatal for outboards,Have you tried priming bulb while running?plugs should be cleaned and regaped every year or at least every 100 hrs
 
I did squeeze the bulb when it was running bad and the bulb was hard. That seems to be ok. I did notice when I pulled the old spark plugs that the top and bottom one were much darker than the middle one.
 
Problem not solved!! I had it out yesterday and it ran great for a few hours and then it bogged down again as i was going full speed. I was pulling a tube and had to stop. I shut the motor off, pulled the kids in and when i started it back up it ran fine. It tried to bog several other times but quickly released. This is driving me crazy i can't figure it out.
 
So I have been anything but impressed with this forum and the help I have received but what did I expect I guess. Anyway after taking the boat out numerous times after I changed the plugs it continued to give me problems. That's when I realized it had to be a short in one of the spark plug wires. I replaced all three of them last night and took the boat out again. It worked flawlessly but time will tell if this was truly the problem. I am 99% sure it was but we shall see. I wanted to follow up in case there are guys like me in the future that have the same problem. Good luck Fellas!!
 
Once again I discovered after running the boat for awhile that it was STILL bogging down. After doing more research and reading about the coils I realized that those could indeed be the problem. Apparently as the coils heat up if there is a crack they can cause the exact problem I was having. My boat would run great for awhile and as it heated up that's when the bogging would begin. Well I changed all three coils. It was simple and easy!! Boat now runs great. In fact I think it runs better now than it ever has. Hope this helps somebody!!
 
Thank you for posting your outcome. Beings we have motors that are more like a fine watch, I find that there too many things that can apparently raise up and bite your butt. I started, with the advice of forum members, a systematic rehab on a 77 Merc 500. All I could do is throw money at it and make sure that all things were needed regardless of the final test to see if "that" solved the problem. I needed help in the worst way and got much of it from a retired marine mechanic. But, he had a life too, so I sought help when he couldn't from the forums. He brought over a puller for the flywheel so I could change the stator. That solved the problem, but I also replaced many needed items in the time I messed with it. It was all good and now I can buzz eight miles instead of crawling. The guys that helped on the forum were excellent and my mechanic was amazed that they spent the effort to help out. They don't have a real high pay scale- Mike
 
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