[endevour]

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

 

[JSL3]

I'd suggest reading through this thread.
http://www.sailnet.com/forums/diesel-engine-forum/55720-yanmar-black-smoke-exhaust.html
It may have your solution or give you some ideas on which way to continue in your search for answers.

 

[captbillc]

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?

 

[endevour]

it overheated one time, ive trying to recreate the overheat but it hasnt happeened again.....i will check the prop though thank you

 

[endevour]

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

 

[MJBrown]

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
Mike

 

[JSL3]

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.

 

[mitiempo]

Could it be a restricted mixing elbow?
Brian

 

[endevour]

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

 

[TSOJOURNER]

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.

 

[mitiempo]

There was another thread on this or another forum with the same problem. Turned out to be the mixing elbow. Good rpm with no load but not able to reach high rpm under load and black smoke of improperly burned fuel. This subject has been covered on the Torreson Diesel forum as well. Restricted air intake will cause the same symptoms. When did you last remove the elbow to check it? I'd check the air intake as well. Both a lot less expensive than injectors as well.
Brian

 

[Northeaster]

1st question: Did it used to rev up to max rpms (about 3600) in gear before, (ie last summer, earlier this summer). If so, then I would definitely make sure the bottom / keel is clean of growth, and the prop is free of growth and rope, etc, before pulling out injectors or exhaust elbows.

Sounds like a classic case of the engine being overloaded, likely due to growth. That does expaling why it doesn't do it in neutral - no load in neutral.

If the boat has never been able to obtain max rpms in gear, I would see if it is overpropped, or then start checking out the other engine / exhaust stuff.

 

[Subsolent]

Motor Problems

Endevour - I have exactly the same problem. Can you tell me what prop you are using. I have a C & C 34 and they have fitted a 16" x 10". When I look at the original specs for the 34 the standard engine was 2QM20 and this is the right prop, but my engine is a 3gm and I have a feeling that the prop should be 18" x 12". I am still researching so if you have found your answer I would be interested to hear it.

 

[endevour]

the problem was solved by cleaning the prop i havent looked up what tyhe original was but its working great right now