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post #1 of 14 Old 09-17-2009 Thread Starter
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motor problems

i have 20 horse power yanmar 3GMF motor. in neutral i can get the rpms up to 3500-4000 if i wanted, however when i put it into gear the highest i can go is about 2000. when i go above that i get heavy black smoke from the aft thru hull. no smoke in cabin or engine compartment. is this an exhaust mainfold problem or maybe a saltwater cooling problem? thank you for any help you can give.
pete
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post #2 of 14 Old 09-17-2009
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I'd suggest reading through this thread.
http://www.sailnet.com/forums/diesel...e-exhaust.html
It may have your solution or give you some ideas on which way to continue in your search for answers.

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post #3 of 14 Old 09-17-2009
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you should not be getting black smoke under load. your engine is overloaded. you may have a line wrapped around the prop, bent blades, some other drag. i don't think it is a plugged up air cleaner because you can get up to high RPM in neutral. is the engine overheating?

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post #4 of 14 Old 09-17-2009 Thread Starter
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it overheated one time, ive trying to recreate the overheat but it hasnt happeened again.....i will check the prop though thank you
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post #5 of 14 Old 09-17-2009 Thread Starter
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wow..jsl3 sounds like we had the same problem.....i scraped the bottom in june. looks like im going back down this weekend...what did you use to scrape..spackle knife? is there anything better......really would like to do this in the water
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post #6 of 14 Old 09-17-2009
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Check the bottom of the keel as well. It always seems to be an area prone to barnacles, especially if you touch bottom every now and then
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post #7 of 14 Old 09-17-2009
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Quote:
Originally Posted by endevour View Post
wow..jsl3 sounds like we had the same problem.....i scraped the bottom in june. looks like im going back down this weekend...what did you use to scrape..spackle knife? is there anything better......really would like to do this in the water
In my case, I had the boat hauled and we cleaned it when it was on the slings. In the future however, I will be using a paint scraper or small drywall knife, wire brush and gloves while I’m anchored somewhere outside the marina.
Since this incident early in the summer, I have been under with a mask and snorkel at least 4 times and found no marine growth. From doing a little research, I’ve found that the barnacle life cycle growth in my area seems to explode around the end of June or so.

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Last edited by JSL3; 09-17-2009 at 09:05 PM.
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post #8 of 14 Old 09-17-2009
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Could it be a restricted mixing elbow?
Brian
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post #9 of 14 Old 09-17-2009 Thread Starter
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yea i scraped it twice this summer on its mooring the second time i really didnt get the prop though so...... we'll se tomorrow. thanks for the help
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post #10 of 14 Old 09-18-2009
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I would replace/rebuild both -(all three?) - injectors. One of them is flooding fuel into the chamber.

Black smoke: Fuel
Blue Smoke: Oil

Pull them all out. Take them to a diesel shop for testing and rebuild. It's a fairly easy job getting them out and then back in.

Not sure why this problem doesn't appear with no load, but it doesn't.

Hopefully, one of them will not check out, because if they all check out then you have a REAL problem because you have at least one cylinder that isn't firing properly.

When you come to a "Y" in the road, take it....Yogi Berra
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