3.0L MerCruiser, idle trouble.

[DiegoSlapstick]

I have a 3.0L MerCruiser that I am having problems with. It will start up and run fine for the first trip around the water. After we park it and hang out for a while it will have a hard time starting and idleing. Once we take a few breaks on the lake it will get to a point where it won’t start at all.
Here is a list of things I have done to it:
1) Changed oil and oil filter
2) Changed fuel filter
3) Changed plugs and wires
4) I have also tried to adjust the idle screw to see if it was too low.

Pictures below.

 

[Scott Danforth]

first, welcome aboard

what troubleshooting have you done?

have you inspected the quality of the fuel in your tank? have you changed the water separating fuel filter?

have you tested the anti-siphon valve?

have you verified your choke works?

what are your compression numbers?

is this a new to you boat with the problem, or is this a new problem with a boat you have owned for a while.

what is the engine temp? have you done a bellows inspection and raw water pump service?

 

[DiegoSlapstick]

Thank you for the warm welcome.
I honestly didn’t know where to start but I did change the fuel water separator to see if that would help and it did not.

I will check Anti-siphon valve next and verify that the choke works. Do you have any details on the anti-siphon valve?

This Boat is new to me, but is a recent problem. It was my mothers boat last season and we did not have this problem.

Engine gets to running temps around 150-175 and doesn’t get higher than that. I recently replaced the shift cable bellow, because it was damaged. Checked all other bellows and no damage was seen.
I have not done a raw water pump inspection.

 

[alldodge]

Welcome
In most cases it will deal with a carb issue. Needs to be cleaned/rebuilt or choke is hanging

I would start by removing the fuel filter and dump the contents into a clear container. There should be nothing but clean gas.

When motor won't start, remove flame arrestor and see if the choke on top of carb is fully open. See if fuel is dripping down carb when motor is off

 

[Scott06]

Would also mention checking fuel system for contamination. That carb is an aftermarket version of a mercarb so it’s second time the boat has had carb issues. Would verify fuel system contaminants are not gumming up the carb

 

[DiegoSlapstick]

Ok, I checked the check valve at fuel tank and it was working correctly.
Cleaned out all fuel lines.
Replaced mechanical fuel pump.

I think it is better but it is still having an idle issue. I think if it was in the water it would die out.

I have attached two videos.
The first one is first start up and the idle is good for 30 minutes.
The second video is at second start up and idle is up and down. I think if it was in water it would die out.

 

[alldodge]

The vids are not attached

 

[DiegoSlapstick]

My apologies, it wouldn’t let me post whole video. Too big so I had to shrink down.
You will notice in the second video how the idle starts low and then get back up to 1100. This is on muffs.
View attachment IMG_8909.MOV
View attachment IMG_8910.MOV

 

[dubs283]

1100 is too high an rpm for idle speed in neutral. You want around 750ish in neutral, 650ish in gear on the water

What is the idle timing set at?

Carb looks way aftermarket, unsure if I'd have confidence it is of sound quality

 

[DiegoSlapstick]

1100 is too high an rpm for idle speed in neutral. You want around 750ish in neutral, 650ish in gear on the water

What is the idle timing set at?

Carb looks way aftermarket, unsure if I'd have confidence it is of sound quality

I had to turn the idle screw in to turn it up to 1100. At 750 it would get so low that it would die out.

I should just bite the bullet and find oem carb?

 

[alldodge]

Carb needs a good cleaning, but buying another works most times, just cost more

 

[DiegoSlapstick]

B

Carb needs a good cleaning, but buying another works most times, just cost more

Bought a rebuild kit. I’ll rebuild it and see what happens.
Keep it posted.

 

[Scott Danforth]

B

Bought a rebuild kit. I’ll rebuild it and see what happens.
Keep it posted.

If you make sure all passages are clean (pass fishing line thru them). And you set the car. Back up correctly, it should be night and day difference

 

[DiegoSlapstick]

If you make sure all passages are clean (pass fishing line thru them). And you set the car. Back up correctly, it should be night and day difference

Do you have a link to a video of how to set up carb correctly? First time rebuilding a large carb like this.

 

[Scott Danforth]

Do you have a link to a video of how to set up carb correctly? First time rebuilding a large carb like this.

I learned to work on carbs almost 50 years ago. I suggest getting an OEM kit (has instructions) or get the factory service manual. Also check out mikes carb site

 

[alldodge]

Agree Mike's carbs has lots of info and he is great to answer questions
IMO
There are lots of you tube vids, but only a few show cleaning and cleaning is the main part. If it's real clean everything thing else is a slight adjustment