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Discussion Starter #1
If you have followed my posts about Sea Foam, you know my 9.9 4 stroke will not slow down without quitting at around 2,200 rpm. I ran a lot of Sea-Foam through it with no luck. Now we have taken the carburetor off and cleaned it and the jets. We also checked the hoses and fuel filter and they seem okay. The fuel pump seems to be pumping if we turn the motor over without starting of course.

I'm out of ideas. This is a 2008 motor and has never given a bit of trouble until a little over a week ago. The boat is out of the water now so it can be worked on without losing parts.
 

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If you have followed my posts about Sea Foam, you know my 9.9 4 stroke will not slow down without quitting at around 2,200 rpm. I ran a lot of Sea-Foam through it with no luck. Now we have taken the carburetor off and cleaned it and the jets. We also checked the hoses and fuel filter and they seem okay. The fuel pump seems to be pumping if we turn the motor over without starting of course.

I'm out of ideas. This is a 2008 motor and has never given a bit of trouble until a little over a week ago. The boat is out of the water now so it can be worked on without losing parts.
I had same problem with my 2007 merc 9.9 4 stroke so I cleaned carb and discovered a small longitudinal crack in the fuel line at the carb. It was real hard to spot, but if it was sucking air, that was the problem. I squeezed the hose and found the crack. I checked fuel filter but it was discolored a bit but not blocking flow. How about a leak around one of the gaskets and spacers that were a challenge to line up for the two bolts? I assume linkages, idle adjustment, fuel mixture (screw behind brass cap) didn't get loose or improperly adjusted. Plugs look good? So there are my ideas, good luck.
 

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Discussion Starter #3
The screw behind the brass cap could be a problem as I will have to drill out the protective plug. I have read of others having to clean out that area. Guess that's my next thing to try.

I do tend to think this was caused by bad fuel as once it started it kept getting worse until the motor would not run at slow speed at all. The only way to start it is to run the throttle up and start it at high speed.

I sure hope I can get this solved as fishing season is slipping by in a hurry.
 

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Discussion Starter #5
Okay. We have cleaned the carburetor, cleaned the jets, cleaned the needle valve, used new gas with no ethanol, a new tank & new fuel hose. It still will not run slow. I am out of ideas. This is a 2008 motor that has never given me a minute of trouble until this happened almost 2 weeks ago.

I am stumped!
 

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The Original Hot Rod
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I had the same issue 2 years ago with my 2008 9.9 Big foot. I had added a couple of oz. of seaform to the portable tank the day before. Went trolling the next day about 10 miles out and the 9.9 died and would not re-start. When I got it back to the dock and tried to restart using starting fluid, it would start but stalled at lower RPM.
Fortunately, there is a marine mechanic in the camperground and he disassemble and cleaned it. He soaked the jets and valves over night after cleaning ultrasonically.
Reassemble the carb and reinstalled and still didn't work...! :mad:

After $400+ and a new carb it's running just fine. Maybe it's just me but seaform will not be going back through that 9.9. ;)
 

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Discussion Starter #7
We tried so many things I'm not sure exactly which cured the problem, but I think it was my friend's final carburetor cleaning that did the job. This time he disassembled it further and did a more complete cleaning. After he put the carburetor back on I hit the key and the motor purred. We adjusted the rpm down to the slow speed and it kept on running. I shut it off and fired it back up again with no problem. It seems to be running smoother than ever.

My guess is that the problem started with bad gas that clogged something in the carburetor.
 

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1950's Outboards Rule
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We tried so many things I'm not sure exactly which cured the problem, but I think it was my friend's final carburetor cleaning that did the job. This time he disassembled it further and did a more complete cleaning. After he put the carburetor back on I hit the key and the motor purred. We adjusted the rpm down to the slow speed and it kept on running. I shut it off and fired it back up again with no problem. It seems to be running smoother than ever.

My guess is that the problem started with bad gas that clogged something in the carburetor.
glad you got it fixed !
 

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Bass & Catfish Charter Service
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The carburetors on these are junk. I've had two new carburetors installed onto my 2008 4-stroke 9.9 Mercury Big Foot. And I've been very disappointed with this Mercury's performance. I've had one problem after another with mine.
I hope you've got it running alright. But if it fouls up again. You might need a new carburetor.

Good luck.
 

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Discussion Starter #11
I had two of those mercs sold it and bought a yamaha T 8. best motor I ever owned,
Interesting because I had a junk Evinrude that I replaced with the Mercury. This is my 5th year with the Mercury and the first trouble I've had. The Evinrude needed the carburetor taken apart and cleaned every spring. I hope this is the last major problem with my Mercury.
 

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I'm no expert, but with a little common sense a new motor can last many years. Every fillup I use a couple ounces of sea foam, and marine stabil. Even if I think I'll use all the gas today, it usually ends up staying in the boat, and 3 months later I'm trying to fire it up. With today's ethanol mixtures, gas loses a lot of its power in 60 to 90 days. If its sits from spring to fall, I dump it on the bonfire. I only go out a couple of times a year, and I'd rather pay a bit more to not have any problems. You have to add stabil at the beginning,so it can help slow down the chemical breakdown. Adding months later before you use it will accomplish nothing. I also disconnect my fuel hose and run my outboard dry before loading it each time. That gas sitting in your carb will go bad quickly, especially if your motor is outside sitting in the sun, or in a stuffy garage for a few weeks. The newer carbs can clog up really easily, and as a result, takes way more maintenance than the old 2 strokes we all know and love.
 

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In regards to the seafoam comment, the reason it caused it to not work at all, is your gummed up deposits were so bad, that when it began to break them down, some got stuck in the narrow fuel passages. If properly maintained, seafoam wouldn't have caused it to stop. If seafoam is causing your exhaust to be a blue smoke, then it's most likely cleaning your fuel system of bad stuff, and your engine is burning it off. That is the point of it, and I would say its working.
 

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Discussion Starter #15
I also am no expert and it is amazing the info I get on this site & others when I have a problem. Most of the posts make Sea Foam sound so good I was planning to put it on my breakfast Cheerios. Then I find a few that say Sea Foam is the root of all motor troubles. :D

I think my problem was from old gas and an old fuel tank. After my buddy cleaned the carburetor twice the motor purred when I launched the boat last evening. From what this non-expert has learned, the jets in a 4-stroke are small and you need to be extra careful with fuel. I bought the gas I now use at the marina as it has no ethanol. It's $4.35 a gallon, but worth it if my motor runs. ;)
 

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Seafoam, Read the MSDS sheet.

It is naptha and pale oil, it is the pale oil that smokes when burnt in the combustion chamber. StaBil is 99% naptha but has no pale oil, thus no smoke.

I'm glad you like it.
 

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Discussion Starter #17
Seafoam, Read the MSDS sheet.

It is naptha and pale oil, it is the pale oil that smokes when burnt in the combustion chamber. StaBil is 99% naptha but has no pale oil, thus no smoke.

I'm glad you like it.
Sea foam did not clear my obstruction, but I think I'll just use the non-ethanol gas from the marina so I might not need any additive. I'll keep using the cheaper gas station stuff in the mowers and my Mule, so I probably should use an additive in them.

I'll also stick with milk on my Cheerios. :D
 

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I had one of these motors. There is a recall on the carb. I went to buckeye out doors, and they had a repair kit for it. My problem, was hard to start and idled high all the time. They put the kit on for FREE, and then it was game on.
I dont use sea foam. Dont believe in it. My opinon. I store my 2 mercs in garage, and dont have problems with them. Thank goodness. Good luck.
 

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That links makes absolutely no sense. It looks like they are just trying to drum up business for their products. I'll stick with the fact I've fixed a myriad of small engines simply by adding seafoam thru the carb. If your getting smoke in your exhaust your either burning old gas or added too much seafoam. To each their own, I'd prefer less demand for the stuff, it's risen in price dramatically the last few years. Either way, fresh gas is the key, ethanol is ****, and shouldn't be in our gas for boats.
 
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