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Old 24 September 2022, 20:45   #1
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Country: South Africa
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Length: 5m +
Engine: Yamaha 55HP 663
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Yamaha 55AE 663 Starting problems

Good day

I would like to find out if anyone can please assist with troubleshooting my Yamaha 55 663. I bought the motor as I wanted to use it on my fishing boat. The motor was standing for at least 3 years. I fitted it to my boat and started checking the basics. First, I removed the spark plugs and added some oil to the cylinders, I then left it for a couple of hours and then turned the motor over by hand to make sure the motor is moving freely.

I then checked for spark on both spark plugs, and the spark was good. I added fresh fuel, primed the primer bulb, connected a battery and tried starting the motor. The motor was cranking for some time and then it fired up, the motor was idling fine and then I tried to rev the motor a few times and it just died, I then tried starting it again and it wouldn't start.

I then removed both carburetors, cleaned them out, checked every jet as well as the jet on top of the carbs. Everything was clean and there were no blockages when pushing air through every passage. I then refitted the carburetors and set the air screws to 1 1/2 turns out. I also checked the fuel pump; the diaphragm was looking good and there was no damage to it.
Next, I added fuel and tried starting it, but it would not start. The motor was flooding for some reason, both spark plugs was wet with the excessive fuel from using the choke.

Today I spent a few more hours trying to start it and it would not start, I then decided to replace the sparkplugs, I couldn't find NGK BR8HS-10 here in South Africa, I then purchased NGK B8HS, I set the spark plug gap to 0.90mm. Next, I fitted the new spark plugs and tried again to start the motor. After pulling the manual choke and setting the idle throttle on the control box to nearly 100% it fired up, I then slowly reduced the idle throttle and the motor was idling good for a couple of minutes, I then tried to rev the motor and it died instantly. I then tried starting the motor and it will not start unless the idle throttle was at 100%, it idled again for some time, I then set the air mixture screws to 1 3/4 out and tried to rev the motor up again, it did rev up, I then switched off the motor but when trying to start it again it refused to start, I had to pull out the choke and idle throttle at 100% then it started again.

I cannot get the motor to fire up without the idle throttle being at 100% and it does not make sense why the choke is needed when the motor was warm.

I also did a cold compression test and I think part of the problem is the difference in compression, the top cylinder is reading 100psi and the bottom cylinder is reading 130psi.

Any advice will be highly appreciated. Another problem that I'm facing is that spare parts for this motor is not easily accessible here in South Africa.

What I understand from the guys in South Africa is that this motor is very reliable, rugged and light on fuel.

I would like to have it running properly.

Thank you
Regards
Daniel
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Old 24 September 2022, 21:35   #2
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I recently bought a boat because the Honda outboard wouldn't run and the guy couldn't figure out why. He had even torn the carbs down. I tore them down again, ran them thru the ultrasonic cleaner, and after putting it back together the motor runs beautifully. Did you remove every fitting inside the carb? The smallest piece of debris can cause running issues.

Easiest test for fuel is to use starting fluid and see if the motor runs. Adding propane is another way to test for lean running.

If the priming bulbs works and fills the fuel bowls, and it still isn't getting enough fuel there is either a vacuum leak or the carbs are the problem.

Cleaning carbs with very small orifices is a total pain. I have small wire doohickeys similar to welding tip cleaners that work great for pushing debris from jets. High pressure air, nasty chemicals, and an ultrasonic cleaner work wonders.
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Old 24 September 2022, 21:48   #3
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Country: South Africa
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Hi Peter

Thank you so much for the reply, I stripped down both carburetors and removed all the jets except for the jet on top of the carburetors that is covered with a cap, I removed the cap and soaked the carburetors for some time, I then took a pressure bottle with liquid and pushed it through the jets, I will give the small doohickeys a shot and see if it helps. I will also check the vacuum lines, if I recall correctly, I have only seen one vacuum line on the bottom carburetor. The top Carburetor doesn't have a vacuum line attached to it.

Thank you, much appreciated.

Regards
Daniel
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Old 25 September 2022, 01:36   #4
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You MUST use high pressure air to flush everything out. A jet can look fine even using a flashlight, but a tiny and I mean tiny piece of debris can cause an issue. A can of carb cleaner sprayed on/in, then blown out with high pressure air can usually get the job done. Hopefully you can get access to high pressure air. Today they make nice light air compressors that work prefect for home projects. Using a piece of wire like from a small bristled brush, can be gently used to probe the jet holes. The carb must also come completely apart! Not a single jet or passage not removed and cleaned. Of course the butterfly shaft stays in place.

I prefer this type of blow gun. A rubber tip is the best way to force air in.


Vacuum leaks can be hoses, but often the gaskets/seals are the leak. Pretty hard to test for vacuum leaks. I use a smoke machine for vacuum leaks by working with the engine off, plug off carbs etc, and at .5 psi it blows a thick smoke in. Finds all kinds of leaks. Otherwise carb cleaner sprayed around the gaskets will often lead to an RPM change that is repeatable for verification.

To be clear hearing that high pressure air wasn't used I would recommend rebuilding the carbs before doing anything else. Then come back and tell use how it's doing
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Old 25 September 2022, 13:54   #5
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Hi Peter

Thank you for the information, I will remove the carburetors this coming weekend, I have access to compressed air as well, I will take the carbs apart and clean the jets and passages, there is however " the housing where the needle sits in", I wasn't able to remove it from the carburetors, I was concerned that I will damage something by pulling on it.

I will keep you posted as things progress.

Once again thank you for your assistance, its highly appreciated.

Regards
Daniel
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Old 25 September 2022, 17:00   #6
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Quote:
Originally Posted by Daniel0202 View Post
there is however " the housing where the needle sits in", I wasn't able to remove it from the carburetors, I was concerned that I will damage something by pulling on it.
Got a photo of said hard to remove part? Maybe one of us can come up with a recommendation for an easy to remove it. If you mean the mixture screw cover and mixture screw then yes it must be removed. Otherwise maybe it is not a part that needs to be cleaned? Like an idle adjustment screw that has nothing directly to do with fuel mixture.
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Old 26 September 2022, 19:01   #7
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Maybe a post or two late here, but I had remarkably similar issues with one of these back in the day.... From memory, a blip of the choke whilst opening the throttle cured it, and I ended up adjusting the idle mix screw by a tiny bit of a turn - it was super sensitve to adjustment, and it was literally 1/8 of a turn and it as you describe,m died on opening the thrittle (overcome by a blip on the choke) , or slightly too rich & before you know it it had oiled up at idle.

Having said that, cleaning the carbs won't do it any harm, but that idle mix adjuster is bonkers sensitive... (Or at last it was on mine!)
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Old 29 September 2022, 15:48   #8
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Hi 9D280

I will give it a shot this weekend, thank you for the information, its much appreciated.

Regards
Daniel
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Old 29 September 2022, 15:57   #9
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Hi Peter

Sorry for my late reply, I was traveling fora few days, the part that's difficult to remove is called the valve seat, unfortunately I couldn't upload a picture here. The needle and seat are sliding up and down in the valve seat. How do I remove it? there is a screw and a small plate that holds in in place and but removing the screw and small plate it's still very tight and I'm concerned I will damage it when pulling on it.

Thank you
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Old 30 September 2022, 00:55   #10
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Grab a clear photo and I am sure we can come up with a solution for you. For instance a stuck jet is best removed with a quality screwdriver that fits tight. Most good screw drivers like Snapon's have a portion near the top to put a wrench. Push down on the screw as hard as possible, completely vertical is important, and use the wrench. There are other tools called impact drivers you hit with a hammer. The screws either break or come loose. You could try spraying some penetrating oil and leave it over night too.

Not sure our English definitions are the same or maybe I am not understanding how your carb works.
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