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motor problems

1886 Views 13 Replies 8 Participants Last post by  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.
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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.
1 - 1 of 14 Posts
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