1997 Merc 5.7 LX overfueling?

[guffins fisherman]

Well, it looks like I will be missing the walleye opener this weekend.  Here's why.  The last time I was out on my boat, powered by a '97 Mercruiser 5.7, I noticed two things:  first, when I started it, there was quite a bit of black smoke(not blue) coming out of the exhaust, second, when trolling at just above idle I noticed a gassy, oily sheen on the water behind the boat.  It was running fine.  Temp was good.  Oil pressure good.  All things normal.  I stopped and revved it up in neutral and it put out a massive float of carbon on the water.  

 

It looks to me like it is overfueling and loading up the cylinder heads.  Funny part is, it is performing great. Starts right up.  No loss of power, no coughing or hesitation to plane and runs like hell across the water.  Ethanol free fuel always and fresh this year, and a fresh oil change this week.   We are thinking maybe cap and rotor, maybe timing chain needs to be replaced.  Hour meter reads 2100+, and was unplugged by previous owner.  

 

Any thoughts?  

 

Matt

[Chas0218]

carbed motor or efi? I would throw in a new set of plugs too. Double check your plug gaps when you pull them.

 

Sucks to hear you are missing it, Can you putter out on a kicker and still fish? I did this once when my big motor was acting up.

Edited May 5, 2016 by Chas0218

[lakebound88]

Heck a cold spark can cause that. Time for basic tune up first. I would check my cap and rotor. The caps like to grow during the winter! Lol. Had same issue on friends boat. Basic tune up fixed it. Good luck

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[guffins fisherman]

I am hoping cap and rotor too, and a set of plugs will do her good. We are going that route first.

Chas, carbed motor. I don't have a kicker. Yet.

[Chas0218]

If the basic tune up doesn't fix it get a 5 gallon can and some tubing and run 3 gallons of non eth gas and 1 bottle of sea foam. Run it thru the carb, sounds like you could have some build up in your carb. Problem with carbs is when they are tuned for WOT at idle they are usually a little rich which might be what you're seeing. 

[guffins fisherman]

Chas, thought about that too. All good suggestions. I will be working on it in Sawmill Bay at the CYC. You may see me out on the bay in the afternoon.

Thanks all.

[Chas0218]

Let me know if you need a hand or someone to bounce an idea off.

[guffins fisherman]

Let me know if you need a hand or someone to bounce an idea off.

thanks. Good luck out there. Leave a few for the rest of us.

[guffins fisherman]

Installed new cap and rotor this afternoon. It seemed to idle cleaner. I idled around a bit to simulate trolling and then gassed it in neutral. No floating carbon or gassy sheen on the water. I bought plugs for it, but didn't swap them out yet. I wanted to do one thing at a time. My dad(career diesel, gas engine and heavy equipment tech) didn't like the look of the inside of the distributor. The yellow $hit flakes off into a dust like corrosion or something. I cleaned out what I could and blew it out. Any thoughts?

[lakebound88]

What did the cap look like?

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[guffins fisherman]

What did the cap look like?

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it was clean, with a little corrosion on each contact.

[lakebound88]

That can cause it... Doesn't take much.

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[guffins fisherman]

I thought maybe. It seemed to fit the distributor looser too. It may have been just plain worn out. It was Merc brand. May have been original. Thanks for the help.

[Chas0218]

I was going to say that cap looked rough, looks like you are set. Looking forward to seeing you out there!

[guffins fisherman]

I was going to say that cap looked rough, looks like you are set. Looking forward to seeing you out there!

oh yeah.