Need advice! Mercury 9.9 HP 4 Stroke running poorly

[chousner]

I have a newer (2000) Mercury 9.9 HP 4 Stroke engine. Just last weekend, I took it out for the first time this year. Just some additional background information: The motor has been sitting for a year and half, I was using it with a new fuel can with brand new gasoline (purchased that day) in it. On Saturday, it ran perfectly. Four hours and no problems. Sunday morning, when I started it up. It seemed like it was running on 1 cylinder instead of two. The idle was rough and the engine’s power was significantly diminished. I had the local mechanic take a look at it. He pulled the plugs, which were quite fouled, and replaced them. Problem fixed… for two hours. After two hours of running beautifully, it started running like crap again. Any suggestions on where to start with this problem? I have not pulled the plugs yet, but I imagine they are fouled again. Does this sound like a carburetor problem? Should I begin by cleaning out the carburetor with Gumout? Any help would be greatly appreciated. <br /><br />Thanks, <br /><br />Chuck<br /><br />a.k.a. Tired Old Dog

 

[chousner]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

Anyone have an idea what's wrong with this motor? <br /><br />Thanks, <br /><br />Chuck

 

[bassboatbuster]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

Napa sells a fuel additive called Sea Foam, it's a great carb cleaner, and "Sea Foam" also make a spray called deep creep.. I'm not sure if it will fix your problem, but a clean Carb never hurt anything

 

[BassMan283]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

My guess since it sat so long there was probably a little gas left in thecarb that turned to goo. The new gas loosened the goo. A carb rebuild should clear it up.

 

[greasemonkeyozi]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

Might not have to worry about rebuilding your carbs, but it wouldnt hurt. Take your cars off, and blow air with your mouth through where the fuel line connects. Should get a good flow.<br /> Inspect for any type of tar like stuff clogging any ports.<br /> Yes, Sea Foam Deep Creep is the best stuff to use on outboard motors. You can get this stuff at NAPA. Take your plugs out and spray a good amount in each cylinder. Let set for a couple of hours or overnight. Hook up your muffs and start next day. Spray some in carborator while running and watch all kinds of nasty stuff blow out your exaust.

 

[The Marine Doctor]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

4 stroke engines must have a fuel stabalizer added to them at the end of each year and it must run with it.<br /><br />The carbs gum up alot easier than 2 stroke engines as the jets are smaller.<br /><br />TMD

 

[chousner]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

Thanks for everyone's input. I will try the Seam Foam and the Deep Creep route first. <br /><br />Regards, <br /><br />Tired Old Old<br /><br />a.k.a. Chuck

 

[BillP]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

It wouldn't surprise me if your valve seats are pitted and causing combustion problems. My 50x4 stroke's valve springs started rusting at about 3 months without running...I can't imagine what they would look like after 1 1/2 yrs of storage without being prepped correctly. I'm on the coast of Florida so these problems are magnified compared to other places.<br /><br />Have you done a compression check?

 

[abr19096]

Re: Need advice! Mercury 9.9 HP 4 Stroke running poorly

Same problem here with a tiller shift 2006 9.9.

Any suggestions on primary set up after I soak clean and rebuild. All of my hoses have cracked at the fittings, not a happy thing for less than 30 month old engine.

Any idea what the purpose of the hose exiting the top of the carb??

Thanx in advance