mercruiser 3.0 idle help needed

[kd7isf]

Hi all,

I've got a brain scratcher going on here and hope someone will chime in and help me out.

I'm helping a friend get his boat running again after several years of storage....

1997 mercruiser 3.0l

Engine runs GREAT above 1200 RPM.
Engine runs ROUGH between 800 and 1200 RPM
Engine runs REALLY ROUGH below 800 -- it "dances" if you will
Engine is VERY hard to start...

This is on the muff.....

Here is what I have done so far:

1. First thought was an ignition issue. We replaced the plugs (looked fine, worn, but normal coloration), replaced the wires, replaced the distributor cap and rotor, and replaced the coil (it was probably good, but it was very corroded....). We also tested the pickup coil in the distributor....

2. Second thought was the carburetor.... More specifically the idle passage.... Took it apart and blew carb cleaner through the idle passage and pretty much every other passage in there.
It should be noted that it did not run below 1200 rpm until after cleaning the carb, setting the float level to 9mm, and setting the idle screw to 2 3/4 turns out. It still seams like a plugged passage, but if that's true, how come I can freely squirt cleaner through it? This one has the spring loaded needle and seat...

Any ideas or thoughts would be much appreciated.... Thanks!!

 

[dubs283]

Re: mercruiser 3.0 idle help needed

have you tried some fresh fuel??

did you change the fuel filters??

 

[Jmunk]

Re: mercruiser 3.0 idle help needed

I recently rebuilt my carb which I believe is the same as yours. Your idle mixture screw is a bit far out, manual states 1 1/2 out, this gives me the impression that the carb is still gummed up. Carb might need to be stripped down and soaked in a gallon can of carb cleaner. When you say you set the float height, you do know that you have to set the height it upside down and right side up with the gasket in place. Where in VA are you?

 

[LilRedNeckGirl]

Re: mercruiser 3.0 idle help needed

Try running the engine on a remote fuel supply, like a portable gas tank. That is not listed in your "what we did so far". Understand, gasoline has a very SHORT shelf life, and "Several years" of storage will render it useless. adding octane boosters and dope will NOT help . Drain and discard, clean tank, replace ALL filters, check fuel lines as gasoline will degrade the rubber lines.
Once you assure its clean fresh fuel getting to the carb, if the issue still exists, then your ready to start trouble shooting. the remote fuel supply is simply a test for the boats fuel quality and system.

 

[kd7isf]

Re: mercruiser 3.0 idle help needed

Hi,

Ok, ya'll caught me on that one.

I should have pointed out that bad gas was actually my very first thought -- and it is currently connected to an outboard tank filled with fresh gas..... We also replaced both fuel filters when we did that....

I should also have pointed out that the owner recently told me he replaced the carburetor with a re manufactured one a couple years ago. It would not run at all before he replaced the carburetor and has apparently had this problem since he replaced it. My inclination is that he should have returned the carb and requested a warranty exchange -- but he didn't know he could do that and now its too late... Warranty only lasts so long....

I agree that the idle screw is way to far out -- but it won't idle at all if I don't do that. I just can't figure how a passage I can blow cleaner through is plugged -- maybe it's partially plugged? I'll try a dip (been avoiding that because I know the dip will remove the paint from it too -- found that out on mine ) It made worlds of difference to mine.

Yes, I know you measure float level with the top upside down and gasket installed -- thanks for pointing that out though, many people don't know that nor do they even know or realize what the little ruler in the carb kit is for..

It should also be noted that the float drop, which many people ignore, is just as important and not properly setting it is a very frequent cause of unexplainable flooding Trust me -- I learned that the hard way...

Profile updated -- I'm in Maryland now (DC Area)

Thanks!!

 

[rickryder]

Re: mercruiser 3.0 idle help needed

You'd be surprised how little of a clog in an idle curcut will make an engine run poorly.... I would soak the carb and recheck everything...Did you set base idle as per the service manual?

 

[kd7isf]

Re: mercruiser 3.0 idle help needed

I tried..... This thing dances so much trying to idle that I can't really get a good idle -- it idles, but barely.

Your right... Hadn't considered that passage as a tuned metering passage... Any little impediment in there changes the mixture... so little fuel moving at idle that .004 inches can make all the difference ..... Thats about 20x smaller then the average spec of dust....

I'll dip it this weekend and see what happens

Thanks

 

[HT32BSX115]

Re: mercruiser 3.0 idle help needed

Howdy Ray,

You definitely have a carb problem OM!

Sometimes you cannot even trust a "professional " "rebuild" !

I would pull it apart and do another "clean"

You want the engine to idle somewhere around 700. Allow it to idle much higher or as high as 1000-1200, and you could damage your drive during shifting and may be harder to get out of gear.



73/Rick

 

[kd7isf]

Re: mercruiser 3.0 idle help needed

I agree -- thanks!
I idle mine all the way down to 450 (electric clutch omc stringer)

I intend to set this one at 650-700 since that's what the book for it says anyway.
Too many perfectly good outdrives are destroyed by idle speeds above what they should be...

 

[airshot]

Re: mercruiser 3.0 idle help needed

A thorough cleaning of the carb is in order, had a similiar problem last year,carb had been rebuilt by previous owner, I rebuilt it again and it idles much smoother!! Also you may want to do a compression check as it sat for some time, if it is up to spec, nothing is rusted and not moving correctly.

Airshot