Sooty Transom - Mercruiser 3.0L

[Almeja]

I have a 2005 Mercruiser 3.0L that is running very rich at idle. Rich to the point that I have a sooty transom. (Note: This is at sea level). She becomes a real pig at my 'regular' lake. (2000 ft).<br /><br />I have the new series carb with the EPA cap over the adjustments (such as they might be). <br /><br />My questions are:<br /><br />1) Are there significant idle mixture adjustments hiding behind the 'magic cap' that would be worth twiddling? (i.e. adjustments that have a significant effect, not just a 'very fine tune')<br /><br />2) If yes on number #1, any advice on removing cap without damage and potential adjustments is appreciated.<br /><br />I have about 4 wks left on warranty... so I guess I could take it to the dealer, but my dilemma is that the nearest reputable dealer (where I purchased the boat) is a 300 mile round trip.<br /><br />If I have to leave the boat a couple days I either have a motel bill or if I go home, a 600 mile trip to get the repair done 'free'... not to mention a couple days down the tubes. <br /><br />I have lots of experience working on engines... but no idea if it's worth it to remove the cap and see if I can make it run better on my own.<br /><br />TIA for any help.

 

[Don S]

Re: Sooty Transom - Mercruiser 3.0L

My guess is your choke is too tight, or inoperative, possibly a wire off the choke coil.<br />This would cause a very rich (Black Transom) Condition. But it probably makes the engine run better because it is too rich. The big problem with the 3.0 is the EPA regulations and what Mercruiser does to "Cure" the problem. running very lean.<br />Read this "Fairy Tale" I posted some time ago.<br /><br />

Let me tell a fairy tale of a 2004, 3.0L Mercruiser engine.<br />Once upon a time a Marine Mechanic had a customer with a 3.0L Mercruiser engine, the engine was very hard to start, hard to keep running till it warmed up and dieseled severely when shut off, even after idling for several minutes.<br />The timing was spot on, and since this engine had the EST distributor was set at the proper timing per the manual and done while in the base timing mode. Still the same problems. It was obvious the engine was running too lean but with the anti tamper devise on the carb mixture screw, it was impossible to adjust it richer.<br />Knowing the lean mixture was probably the cause of many past 3.0L engine failures, the MM (Marine Mechanic) decided, against his better judgment, that the problem with the engine would be a constant problem if not prevented somehow.<br />Knowing full well that the all powerful California EPA may rain fire and damnation on him for the rest of natural born life and on into the unknown after death, the MM decided to take the matters into his own hands and remove the tamper proof cover over the idle mixture screw. He soon found this to be a very difficult task, but somehow managed to remove it without destroying the carb or the screw. (He later found it would have been much easier to order a new mixture screw and just replace it and go ahead and break the old one off.) <br />Finally after the success of removing the dreaded seal, he backed the mixture screw out approximately a quarter to a half turn. the engine then smoothed out and ran great, idled smooth and slower without dieing and was even easy to start for the first time in it's life, even cold, and never dieseled again when shut off. <br />While the MM is worried about the hereafter and the consequences of his irresponsible act against the all powerful California EPA and all the other mini EPA's of the world, along with the consequences of his complete disregard for the Mercruiser procedures outlined in his service manual, the dastardly dead was done...............<br />The customer, however, wondered why his boat was now working perfectly but the poor ole MM was unable to tell him the truth, and worries to this day he will be found out and that upon passing he will be sent to the worst part of purgatory for his serious misdoings, but I will......uh, sorry about that, he will be happy in knowing that the boats engine will now live and last for many trips to the great fishing grounds of the owner.<br />Please understand that this is only a fairy tale and should only be told in the proper company. DO NOT try this at home as you could also be condemned to eternal damnation of the EPA gods.

 

[rodbolt]

Re: Sooty Transom - Mercruiser 3.0L

ya know if ya mess with the EPA controls ya risk your first born and purgatory .<br /> glad I would never have a fairy tale like that .<br /> nope not me.<br /> never cut a plug from the air/fuel screws. none thats provable anyway

 

[Almeja]

Re: Sooty Transom - Mercruiser 3.0L

Thanks for the advice. As it runs now, the boat wouldn't meet pollution standards in Ethiopia let alone the USA.<br /><br />I think I took a look down the venturi before... and didn't see any choke closure at normal operating temperature, but another look wouldn't hurt.<br /><br />Careful use of pliers to remove the plug? <br /><br />Since these carbs can be adjusted by a 'certified' pollution station, I reckon there's either a tool or a technique for getting it out. Hmmm... probably a $200 tool.