3.0L mercruiser running cool

[airshot]

How about a compression check, low compression could cause an issue with acceleration. It is cheap and will give a look at internal health. I am still inclined to believe you have a carb issue if the compression check good. Taking a carb apart and cleaning is no where near a rebuild job. Worn gaskets can cause problems as well as the two screws not getting tight. Any small air leak or do either of those two loose screws control fuel flow thru the carb? Those holes in the carb are very tiny and any little piece of crud can cause a problem. If you read the rebuild thread, just blowing cleaner and air thru a passage is not enough a wire should be passed thru to be absolutely sure it is completely open. I understand your frustration...been there ....done that....better to take each step and do a thorough job so you know full well that step can be eliminated.

 

[Rick Stephens]

If a valve is tight that would also affect compression results. Pretty wide range of acceptable compression, just none be less than 70% of the highest.

 

[sti1471]

I did a compression test on Saturday. I removed all of the spark plugs and tested each cyl 1 at a time.

Each Cyl was around 120 give or take 1-4 psi.

 

[sti1471]

I will take the carb apart tonight and soak it in some cleaner along with running a small music wire through the ports to make sure all the ports are cleaned out.

 

[sti1471]

No Title

OK so I got the carb removed from the engine last night and did some clean up on the parts. It was fairly clean, but there was a few spots on the venturi that needed some attention. However I noticed this 1 hole in the carb that I have never noticed before and I was wondering if anyone can tell me what it is and or does.

It is on the top of the carb, and it runs through to the bottom. the top and bottom side marked in the photos. The reason I am wondering, is because since it passes all the way through the carb it has to have some purpose. The gasket on this carb did not have a hole cut out for that hole. When I google this gasket, from what I can see is that there is a hole for this to do whatever it does. I can drill a hole in the gasket if needed, but looking at the carb, I can't imagine what this little hole really does.

Thoughts?

 

[airshot]

You might try looking at a true Mercruiser rebuild kit for that model carb to see if it has a hole in it. I remember that hole from my rebuilds but cannot say for sure whether the gasket had a hole or not. It could be a possibility that a previous owner did a rebuild and used the wrong gasket. Has the boat ever run perfect while in your ownership? If it ran the way you describe when you bought it, could be the rebuild was not done correctly in the past. Just throwing ideas out there, but let me add this.....being a boater for more than 50 yrs and doing my own work has taught me one thing....NEVER cut corners and always use factory recommended parts as well as following the factory service manual not an aftermarket one. Shortcuts always cost more in the long run..

 

[sti1471]

The boat when I bought it was not running. it was in good shape but the lower unit was removed, as well as some little engine parts. I think the previous owner thought he blew the motor because when I put it all back together it ran pretty bad. Then I found that Cyl 2&3 had 0 compression (which he probably knew). SO I tore it down and found a broken head gasket and now all Cylinders are 115+ PSI.

Anyways back to the issue, NO the boat has never run great since i have owned it. I have never had it on the lake past the no wake zone as all floats have been tests. Now I have completed the rebuild and rebuilt the interior and all and now it is ready to put some hours on it. When I google that gasket all of the pictures I see have a hole cut out for it so I guess I will follow in suit and cut one out for it.

Another thing I found was that the thermostat housing did not have a gasket that sits on top of the thermostat. Looking at the housing, there is a little indented lip that the thermostat sits in to sit flush. There is another indent in the top half of the housing. SO without that gasket, I am thinking that there is about 1/16" - 1/8" that the water could be pushing the gasket up and slipping by. I assume that the gasket it meant to hold the thermostat down and seal water from slipping by.

This might not be the cause of the poor performance, but it very well could account for the engine temp issue.

 

[sti1471]

No Title

OK so I traced that mystery hole in the carb, and it goes through the carb, and lines up with a hole in the bottom part of the carb, goes all the way through that and comes out the bottom near the mixture screw.. The red arrow in the photo marks the end point of that mystery hole. Maybe seeing where it comes out will determine what exactly it does.

 

[sti1471]

I did some research on that hole, and it turns out that it is an air bleeder. it basically is what is responsible for the vacuum for the power piston, as well as air bleeder / corrector for the idle circuit. I will continue to clean all the carb up, but seeing how the gasket was blocking that port, it sounds like it was not bleeding air in the idle passage, as well as not allowing the power piston vacuum to work. that little hole could have been the cause of most of the performance issues!

I will have it all back together tomorrow and hopefully do a test tune on the water muffs and hopefully report back with good news.

 

[Rick Stephens]

That would be awesome!