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Low revs problems

wynjim55

wynjim55

Regular Contributor
My friend has a problem with his 2006 Mercruiser 3.0, it idles rough, has difficulty down low (hesitates, almost dies), but runs perfectly at higher revs. When he slows down from fast running, either slowly decreasing revs or quickly decreasing revs the engine dies. The fuel plunger (inside carb) seems to be squirting fuel in nicely, there is no fuel venting from the bowl into the top of the carb either on start-up or at idle. With the flame arrester/air filter removed you can distinctly hear air being sucked in the large port above the choke housing (electric choke). Where do we start with diagnosing this problem?

The carb has part numbers:
866140001
33 6623
stamped below the main fuel inlet port from the external pump.

There is also a sticker on the outside of the fuel bowl:
SAE J1223
Marine
 
That was the way we were leaning and a rebuild kit has already been ordered, I just wanted to make sure we weren't missing something due to tunnel vision. Thanks for the help.
 
Rebuild kit not a be-all end all. MAKE SURE all the tiny passages in the jets ( especially the idle and low speed) are CLEAN. With the advent of Ethanol, gone are the days of a quick soak and a blow out. Sometimes the residue/crap that the ethanol "gifts" you with only responds to mechanical cleaning (thin strand(s) of wire). If possible, shine light thru from the far end of the jet look into the jet from the other end and make sure walls are shiny. Do not use a drill bit.
 
In Australia we still get the choice of ethanol blended fuel or non. I don't think that will be a problem but regardless I intend to give everything a good soak in some sort of solvent overnight (all trace of gaskets removed prior to dunking) before air drying each component prior to re-assembly. I was thinking of using kerosene to clean everything, any other suggestions?
 
I use lacquer thinner--excellent carb cleaner but VERY DANGEROUS. Use it outdoors since the vapors can kill you quickly by breathing them or by fire.
 
Thanks for you advice on this one guys, it has been fixed for quite a while now.

The rebuild kit arrived and after a good soak in lacquer thinners and after a good air dry it all went back together. The problem has been rectified and it was that simple.

Thanks again.
 
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