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Old 04-06-2010, 17:58   #1
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Outboard Mechanics 101 - Fuel Starvation

At least that is what it's acting like. The motor is a 2004 Yamaha 9.9 2-stroke. Symptoms are: Must choke to start. Always in the first position. Sometimes in the 2nd (all the way out). Once running I can keep it running only with about 1/4 to 1/3 throttle. I can take the choke off and she'll run wide open just fine--plenty of power--but the second I take my hand off the gas and let it go to idle she'll sneeze a couple of times and conk out. She also has a high-pitched whistle (intermittent) which seems to come and go.

What I've done so far: The obvious:
Got fresh gas
Drained bowl--it was clean
checked filter --good flow but cleaned it anyway
Adjusted idle & spark advance
took apart carb and disassembled & soaked in carb cleaner.
Took out both jets and cleaned.
Sprayed carb cleaner in intake.

I've had to choke this motor to crank it from when new and am about fed up with the thing. Any ideas?????
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Old 04-06-2010, 18:51   #2
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Okay I am no outboard mechanic, but maybe it is a weak spark. New plugs gapped correctly, and make sure they spark nicely against the head.
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Old 04-06-2010, 20:08   #3
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What type of carb cleanr did you use?

The Spray stuff doesn't work all that well, plus you have to blow out every orifice/passage. I use Brake-Kleen and Compressed air.

Spraying Carb cleaner in the intake does nothing.
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Old 04-06-2010, 20:12   #4
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Your idle circuit is clogged.

Unless you happen to have bad reed valves - can happen.
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Old 05-06-2010, 05:51   #5
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OUTBOARD MOTORS LEARNER’S GUIDE
http://www.spc.int/coastfish/Section...oard_lg_en.pdf


Some cheap outboard motor service and repair manuals:


Johnson/Evinrude ➥ http://www.readmanual.com/outboard.m...nson.evinrude/

Mercury
http://www.readmanual.com/outboard.motors/mercury/

Honda ➥ http://www.readmanual.com/outboard.motors/honda/

Yamaha ➥ http://www.readmanual.com/outboard.motors/yamaha/
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Old 05-06-2010, 06:35   #6
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Carb woes

If you can get your hands on an exploded view of your Carb you will see the idle and off idle ports ( look closely in the area of the throttle plate). These are quite small and clog easily. Compressed air is usually the only way to clear them as cleaner will not dislodge the dirt. Gasoline with alochol leaves a white crytaline deposit over time and plays hell with these tiny passages. Carbuertors on modern outboards have become quite complicated with circuits not found on the older engines and can be finicky to diagnose. Don't give up.
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Old 05-06-2010, 06:58   #7
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Quote:
Originally Posted by tager View Post
Okay I am no outboard mechanic, but maybe it is a weak spark. New plugs gapped correctly, and make sure they spark nicely against the head.
Thanks, Tag -- I've changed the plugs, twice, also, and they bit me pretty good when I tested the spark. I should have mentioned that.
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Old 05-06-2010, 07:01   #8
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Quote:
Originally Posted by Chief Engineer View Post
What type of carb cleanr did you use?

The Spray stuff doesn't work all that well, plus you have to blow out every orifice/passage. I use Brake-Kleen and Compressed air.

Spraying Carb cleaner in the intake does nothing.
I used a Gunk product one time, Carb medic one time and Sea Foam one time. I also used compressed air on the ports. I'll try the brake clean and compressed air.

I sprayed some cleaner in the intake port in an effort to get some solvent back to the reeds in the thought that perhaps they were varnished up a bit.
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Old 05-06-2010, 07:05   #9
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Quote:
Originally Posted by Therapy View Post
Your idle circuit is clogged.

Unless you happen to have bad reed valves - can happen.
Sure seems that way, doesn't it? I've soaked the thing in carb cleaner and then blown through the little idle-jet supply port with compressed air and have taken the idle jet out and cleaned it twice. It sprays out nicely, so the jet itself is okay and the supply port seems to blow through, too.

How would I check for bad reed valves? Can they be cleaned like the ports? Or must they be replaced?
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Old 05-06-2010, 07:07   #10
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After taking the carb apart, use carb cleaner with the "straw installed" to clean the varnish out of all the passages,jets and reed. Have always had good results with this method. I don't know how many hrs you have on your motor , I had a merc with lots of hrs and it had the same symptoms. Grabbed the flywheel one day and noticed movement (side to side), the crank was shot,junked motor.
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Old 05-06-2010, 07:15   #11
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Squeeze the bulb on the fuel line when the engine is running.If it stalls,replace the fuel pump diaphragm.Tiny holes in the diaphragm let fuel directly into the base through the pulse tube,bypassing the carb.
I had an 8 hp Marriner(Yamaha) withe the same symptoms.$22 fuel pump kit fixed it.

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Old 05-06-2010, 08:43   #12
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Old 05-06-2010, 09:05   #13
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checking reed valves

To check for spit back hold a piece of white card board in front of the carb inlet with the engine running. if fuel accumulates on the card board the reed valves aren't sealing. A timing light also works but most of us don't have one of those in our tool kit.
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Old 05-06-2010, 10:17   #14
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Thanks everyone. I've spent the last couple hours disassembling, soaking, blowing out with compressed air and reassembling the carb. I'm back out to the boat now to give it a check. Will report back!
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Old 05-06-2010, 10:36   #15
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Check the gaskets and fasteners on the carburetor and any intake manifolds. I had an old Johnson with exactly the same symptoms of which you speak. There was a bad seal from carburetor to block. At full throttle, the high vacuum would suck the carburetor closer to the block and seal the leak and the motor would run great, but let off the gas and the leak opened up allowing air in leaning out the mixture and necessitating choking the engine to run. Any loose fitting on an intake manifold could cause the same problem.
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