3.0L 140HP Mercruiser concerns

bohlendorf

Cadet
Joined
Jun 20, 2013
Messages
6
Hey guys! Boating season is right around the corner and I really need a few questions answered about my engine. I changed the oil in my engine with a non detergent straight 30 weight oil. My engine is stamped with SAE 30-SE oil. Did I use the correct oil? Also I changed all the spark plugs in my boat because when I fired it up and gave it throttle it was fine till I started getting up to about 3500 rpms and it would start killing the engine but if I slowly gave it throttle past that point it would be fine and at full throttle it was smooth. So my next question is...could there be any reason why it has that "dead spot" in my throttle? Could is be a dirty carburetor?
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Re: 3.0L 140HP Mercruiser concerns

Hey guys! Boating season is right around the corner and I really need a few questions answered about my engine. I changed the oil in my engine with a non detergent straight 30 weight oil. My engine is stamped with SAE 30-SE oil. Did I use the correct oil? Also I changed all the spark plugs in my boat because when I fired it up and gave it throttle it was fine till I started getting up to about 3500 rpms and it would start killing the engine but if I slowly gave it throttle past that point it would be fine and at full throttle it was smooth. So my next question is...could there be any reason why it has that "dead spot" in my throttle? Could is be a dirty carburetor?

Straight 30W can be OK so long as you boat where the air temp is between 32 and 50 degrees, but no way is NON-Detergent. The non-detergent oil is for very old engines which have a lot of hours/miles on them, things such as 1920 and 30 tractors. Suck that stuff out of there and put regular detergent oil back in. What is your serial number or at least your year

Straight 40W is good from 50 degrees and up

What did your old spark plugs look like?

Getting past a dead spot in most cases is a carb issue, probably needs a rebuild or replacement.
 

79Renken

Seaman Apprentice
Joined
Jul 24, 2006
Messages
35
Re: 3.0L 140HP Mercruiser concerns

Also I changed all the spark plugs in my boat because when I fired it up and gave it throttle it was fine till I started getting up to about 3500 rpms and it would start killing the engine but if I slowly gave it throttle past that point it would be fine and at full throttle it was smooth. So my next question is...could there be any reason why it has that "dead spot" in my throttle? Could is be a dirty carburetor?

Sounds like an accelerator pump issue. A good cleaning and a carb kit should take care of that.
 

bohlendorf

Cadet
Joined
Jun 20, 2013
Messages
6
Re: 3.0L 140HP Mercruiser concerns

Thanks guys for the help, I'm going to try and rebuild my carb this weekend (if it take it)! I have a 1984 Cheetah. But like I said the engine was stamped with SAE 30-SE so what oil would work best with it? Its 140hp 3.0L Mercruiser I/O
 
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