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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3929
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Noel. I have a 2000 9.9 Mercury outboard. Bought it as new

Customer Question

Hi Noel. I have a 2000 9.9 Mercury outboard. Bought it as new old stock in 2005 and ran it for about 10 hours. Then I bought another boat and set it aside. This Spring put on a new water pump and bucket ran it. Primed and started on the next pull. Idled fine. However, during my first outing under load it would miss until I got up on plane. It will run fine for 3 or 4 seconds, then a sort of miss or backfire occurs and a resulting puff of smoke. Afterwards I bucket ran it again. Idles fine. But if I open the throttle a bit, it will periodically stumble again. Someone suggested a new carberator might be in order due to some corrosion from ethanol while it was in storage. But with so few hours it seems counterintuitive to me. Thoughts?
Submitted: 2 years ago.
Category: Boat
Expert:  Charles replied 2 years ago.

Hello. my name is***** will assist you today.

Did you already clean the carb?

Would you please post the serial number of the engine?

Customer: replied 2 years ago.
Carb is near new. Just sprayed it with cleaner. Serial. 0T092513
Expert:  Charles replied 2 years ago.

Did you remove the carb and clean it or just spray cleaner through it?

Customer: replied 2 years ago.
Just sprayed through it while running and not running. Also removed needle valve, sprayed through with supplied straw until it came through the small vent hole on top of carb towards back.
Expert:  Charles replied 2 years ago.

Do you mean the needle vale that is on the side of the carb?

Customer: replied 2 years ago.
There is no cover on this carb. So if you look straight on its a brass screw at 12 oclock
Expert:  Charles replied 2 years ago.

Ok,

I have the diagram open.

Reading your extra info, The gap on the plugs is too much. It needs to be at .040.

does using the primer help the engine run better?

Customer: replied 2 years ago.
I had looked up 10 hp in the service manual, which was .60. My 9.9 should have been .40 like you said. Weird thing is that the plugs I removed were gapped at .60 and .50. New primer ball, checked the installation. It will pump up hard while underway, but no change in performance. Why Mercury made a 10 and 9.9 is beyond me. And why my 1968 performed flawlessly until 2005 is beyond me also. I don't expect the same out of this one. Please respond and I'll respond back as soon as I re gap the plugs
Expert:  Charles replied 2 years ago.

I am thinking that since this motor sat for a while, you have a plugged carb. Spraying cleaner through the throat is not doing anything but keeping it running. You will need to remove the carb and take it apart. Clean all of the passages including the jets and the accelerator pump.

The carb gasket kit includes all items except the needle that you will also need to replace. I can talk you through this process.

Customer: replied 2 years ago.
Well...When I took the plugs out, which had about 5 minutes on them, one was oil fouled already and the other perfect.
Expert:  Charles replied 2 years ago.

Was it the bottom one that was fouled?

Customer: replied 2 years ago.
how did you know that?
Customer: replied 2 years ago.
Charles, I don't know if you got my last answer which was yes, the bottom plug. Message said server did not respond.
Expert:  Charles replied 2 years ago.

I work on outboard engines every day. I am not just an online guy. I am a certified Mercury tech with a day job in a busy repair shop.

I am not guessing when I say that you need to remove the carb and clean it.

Customer: replied 2 years ago.
Sorry, I didn't mean to question you. I was busy once myself and always relied on my experts. That is until I acquired a brain injury. Lost my practice, which precipitated in me having to sell my other boat, the one I was going to retire with. So I'm trying to salvage what I can, otherwise I would just bring this to a shop. Just wondering, why the bottom plug. I'll order the kit and needle valve and get back. Would it be for a WBC 47A?
Expert:  Charles replied 2 years ago.

Do you want the carb kit and needle numbers?

Customer: replied 2 years ago.
thank you.
Expert:  Charles replied 2 years ago.

Needle is 1395-803861

Kit is 9761 1

Customer: replied 2 years ago.
Hi Charles, rebuilt the carb today. Staightforward. However, when I pressurized the ball, I had a leak. As Im sure you are aware, on top of the carb is a cover and gasket. The cover is marked TOP. It appears that the way its constructed, there is a relief vent/spillway sandwiched in between created by an opening in the gasket. Just gushing out. Disassembled and reassembled the diapham pump and compared again to an exploded diagram. Not much to it. Just dont know where to look. Thanks, John
Expert:  Charles replied 2 years ago.
John,
with the carb flooding, your needle adjustment is not correct. You will need to remove the carb and adjust the float.
Customer: replied 2 years ago.
Turns out i had the bail over the needle valve upside down. Fixed it, and could get it started, but it wouldn't idle for more than 15 seconds. I would prime it, it would idle, then die. Repeated the cycle maybe 10 times. So I quickly put it in gear and it would maintain idle speed in the tank in both forward and reverse, but again it would misfire from time to time. Once it got warm, I took it out of gear and returned it to idle and it did so, but a bit rough. Couldn't smooth it out with the idle screw. I put it away and I'll have to cold start it again tomorrow morning and see what happens. I guess I won't know if it will misfire under load until I get it out on open water. Thoughts?
Expert:  Charles replied 2 years ago.

When you had it off, did you also replace the spring under the blue primer diaphragm?

Where is the mixture screw set at currently?

Customer: replied 2 years ago.
I replaced thr spring. I set the screw at 1 1/2 turns.
Expert:  Charles replied 2 years ago.

Ok, So I take it that the ball is still in there?

Is the motor sneezing when you throttle it up?

Customer: replied 2 years ago.
Expert:  Charles replied 2 years ago.

To both questions?

Customer: replied 2 years ago.
to both, check ball is in place.
Expert:  Charles replied 2 years ago.

Alright,

Did you replace the base gasket behind the carb when you had it off?

Can you back out the mixture screw slightly and make the engine idle more smoothly?

Do you know what the compression is on each cylinder?

Customer: replied 2 years ago.
Interesting comment regarding the gasket. The rebuild kit came with a gasket, but when I removed the carb thrre was what looks like a round permanent silicone gasket in a groove. So I didnt use the gasket. Previously I backed out the screw and made no difference until I got to 2 turns, then it choked. I can do a compression test. Meanwhile, what should I do about the gasket?
Customer: replied 2 years ago.
Both top and bottom cylinders top out at 75 lbs. However, the spark plug for the top cylinder was wet.
Expert:  Charles replied 2 years ago.

that is pretty low. Is this an electric start motor?

Customer: replied 2 years ago.
No, pulling it by hand.
Customer: replied 2 years ago.
10 hp
Expert:  Charles replied 2 years ago.

How is the plug for the bottom cyl?

Customer: replied 2 years ago.
Normal
Expert:  Charles replied 2 years ago.

The rubber ring should have been on the back of the reeds, the gasket goes on the front side between the reds and the carb. When installing the gasket, make sure that the hole in the reed block aligns with the hole in the gasket. This is what provides the crank pressure to the fuel pump.