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Old 06-05-2011, 08:59 PM   #1
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Default Black Carbon Soot in Exhaust

Finally a perfect boating day and I appear to have a serious problem. This is first time I started it in 2 weeks. Last time it seemed to run fine. Today I Loaded up for a full day on the water and when I started my boat huge amounts of black soot and smoke came out of the exhaust. I tried playing around with the throttle and the choke on the 4bbl carb as I assume it was running too rich but it did the same each time I started it. I did not run it more than a few seconds each time as the amount of carbon coming out was absolutely huge and I do not want to damage anything. I was dry soot that floated in the water in huge slicks (there was no oil present). The fourth time I tried to start I had some difficulty so I gave up. I am worried I am fouling the plugs.

I have 5.7 Mercuiser with a 4bbl Edelbrock Carb. I am hoping there is an easy fix as it is a huge hassle for me to bring this thing in for service. I am pretty concerned by the massive amounts of carbon.

Any advice greatly appreciated.
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Old 06-06-2011, 12:15 PM   #2
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Cool exhaust

I would pull the plugs and see if there is a lot of carbon on them.If so you will have to deal with to rich mixture .Check choke and be sure it is open also air filter clean .To much gas not enough air plugs will tell you for sure good luck
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Old 06-06-2011, 01:36 PM   #3
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As Cunuck said, pull some plugs. If you've got that much soot coming out of the exhaust the engine is running way too rich and the plugs will show it, they will be a mess. I suspect you could also smell the unburnt gas. If the plugs are black then go ahead and replace all of them - they are not likely to come clean by themselves. The few times you started the engine - was it difficult to get it to start?

Sounds like you may have a stuck (open) float in the carb which is dumping gas into the engine. That, or the choke is stuck closed.

Dan
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Old 06-06-2011, 04:20 PM   #4
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It started pretty easy the first few times. What is weird is that this came on so suddenly. Last time (2 weekes ago) it ran great and then on first start this weekend it started blowing all this soot. I am hoping it is just a carb/choke issue. I do not recall smelling gas and there was no sheen on the water, but everthing I have read points to way too rich mixture. The air filter looks OK. I can't see that causing such a drastic, sudden change. I think something is stuck or disconnected.

I don't know much about carbs, hopefully I can find someone to come out and take a look as bring this thing into town is not practical at this point. I will pull some plugs to take a look, but I don't want to replace them until I fix the issue.
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Old 06-06-2011, 08:13 PM   #5
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Cool carbon

I would start the motor with the air cleaner off and see if the choke plates open all the way and fairly quick 1min.If the plugs are black and fouled there is no point in putting them back .Put new plugs how old are the plugs in the motor??. Be sure to check the plug gap for that motor.
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Old 06-08-2011, 07:30 PM   #6
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Thanks cunuck (and sorry about the game the other night), now that I have read up on carbs a lot more, I will be looking for a faulty choke or float. I won't be able to get back out on the boat until the weekend. This has an electric choke and it is possible I may have disloged a wire when I was filling the trim/tilt reservoir. I will also check that the hot wire has current. I understand the choke is supposed to open a few mm right away and then open right up once it warms up. This carbon soot started coming out immediately so it either is that the choke is not opening at all, or perhaps more likely a float issue.

I also dont want to change the plugs until I know this is fixed or I will just be fouling them again
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Old 06-08-2011, 11:30 PM   #7
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yes they fell apart but it's not over.my elect choke comes off in this weather in less than a minute.You can check it with engine off full ahead to set the choke and leave the key on it should be live to the choke and watch to see it come off.good luck
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