The South Merc 50 dripping some oil from the carbs

Hi everybody from the deep south Argentina,

We own (with my dad) a '90's Merc 50 HP 3-Cyl 2 stroke ELPTO Oil injected
My dad has some background servicing engines, carbs and so. And I'm the electric/electronic geek of the family, so we complement each other

Our engine works like a charm (around 550 hours usage), we bought it used on a Campanili explorer 440 (around 15 ft) locally produced hull, that is very light, so we are getting great performance from the engine without even forcing it, our cruise revs are around 3000-3500 RPM for 40-45 km/h around 25-28 mph, and we get a little less than 2 gallons hour of fuel consumption, so we are delighted of the engine.

Anyway, we have an issue:

- when the engine is tilted and stopped for a while (let's say 2-3 weeks), a small quantity of oil drips from the cylinders trough the carbs and deposits on the engine lower cowling. We hear mixed opinions around here about this issue, but we really don't trust very much on any of the "mechanics" or service centers around here (will explain later on why)
One of the opinions is that oil dripping is actually normal when the engine remains without use and a small leak develops because of gravity trough the oil pump or the remains of fuel-oil mixture on the carbs and ends up on the lower carb or cylinder. The only apparent effect is seen when we re-start the engine and we are observing too much "blue-smoke" due to the enriched mixture containing oil in excess. After a short while the engine is running smoothly again, without abnormal smoke.

A "mechanic" told us that a good way to avoid this is to get rid of the oil injection system and mix the oil directly in the tank (like the old days of the 50:1). We don't like this option:
a- because this system seems to work fine on the engine and is very comfortable and simple to operate, apart of the oil drip when not used, and
b- because we think the manufacturer engineers are less stupid than our "mechanics" friends, and also, the engine has been running for almost 20 years like this without problems, so... why change that?

We were thinking also on a possibility, regarding the oil check valve maybe not closing correctly before the T were oil mixes with the gas, just before the fuel pump:
Item 24 on the fuel system diagram here:
http://www.marineengine.com/parts/mercury_marine_parts/sn/0G291556/1050411SD/1680_120

Maybe oil slowly flows to the carbs because of gravity effect (the oil tank level is higher than the lower carb) due to a failure to close from the check valve. The gasoline evaporates from the system and at the end only the oil remains. Do you guys think we are on the right track over here? or maybe you have already a diagnosis for this issue.

Our distrust on the service centers came from the fact that upon buying the set (hull+engine), we service it on a local official dealer. After a short while, the engine started to cough a low RPM and when on gear sometimes stalled. Dismounted the carbs and found ancient history gum on them. After that, we decided to take the matter in our hands and service the engine ourselves, at least on the normal issues. So, we are replacing filters, transmission oil, impeller change and cleaning the carbs ourselves, and we are sure about the job done, and so far the results have been so much better than "the mechanics" around here.

Currently I'm trying to get a Mercury or a Seloc service manual, but with import restrictions around here, specially on online shopping and delivery, lately is getting hard to buy... so all we have for the moment is what we can find around the internet. This forum has been already of a great help so far, and all your opinions or heads up into any reading material would be of a great help to our little Merc...

Thanks in advance from the south fishing Merc...
good boating and good fishing over there

Just a thought, but when you tilt the engine up this allows the fuel in the carb float bowls to drain from the carbs. As the fuel is already mixed with oil, the gasoline evaporates, leaving the oil.

Well, that was our other hypothesis. But the oil seems to be 'continuously' flowing. A very small amount on a long time of stand still, or at least looks like. If it's only the remnant oil on the carbs, it should stop at some point, right?. No visible leaks other than from the carbs, specially on the lower one, at least looks like this.

Another curious thing: every time we stop the engine, my dad disconnects the fuel supply until the engine stalls from fuel starvation. This is an old habit he has from the old days when the mixture was made on the fuel tank. I'm not sure if this is good on the oil injected model. The oil pump remains pumping oil even if the fuel is over on the pipe. So at the end of this procedure the carbs are full with oil instead of the mixture. Am I right? but you know, old habits are hard to change. Looking at the diagrams, looks like the oil pump will continue to deliver oil until the engine stops 'cause is an engine driven pump.
My dad does this to flush the remaining fuel on the carbs, to prevent it to rot when the engine is stored for a while. Again, this is an old habit from the old days, and I'm now thinking this also could be the cause of the 'excessive' oil presence on the carburetors.

Maybe some other owner of a model like this (oil injected with carbs) can confirm if they have (or had) the same issue?

we'll keep an eye on this matter and if we find more data will post it on the thread.

Another 'pearl' from the mechanical 'service' around here. A 'mechanic' told us... well.. there's no oil flowing into the carbs, the injection is going directly on the cilinders... WHAAAATTTTT???? are you serious????
maybe on the new mercs... not on this one for sure... well, just a quick look at the T after the oil pump, and the drawings... well... that's a mechanic I would not call or recommend... amazing the idiocy and ignorance around here, on the 'self' called 'authorized service'. I mean, i don't know anything about engines, but i can read a diagram or at least look the connections on the engine.
If I'm wrong please correct me... but I don't think so...

thanks in advance on your opinions or heads up

you are on the right track! there is an oil check valve in the "t" hose that begins the mixture. That might be weak,also i won't tilt my motor up to where the fuel is running out!Do Not drain carbs empty! add some fuel storage treatment to the gas to keep it from going bad. it does help,but our gas really sucks these days.I know DaD's are old school,also if you drain them,the rubber in the fuel pump and carbs will dry up and not seal correctly the next time in use.

Thanks Sammy, I think you're right... after a good carbs cleaning, looks like the oil leak stopped, we are now not finding any oil on the cowling. Anyway, I'll try your solution to add some fuel stabilizer or treatment and test it further without emptying the carbs every time. Gasoline over here is really of an awful quality... we suspect much more ethanol than the 8% advertised also.
About the tilting, in the position that the engine and the boat are stored is not possible for us to leave the engine perfectly horizontal, we try our best to leave it as horizontal as possible anyway, and it's working so far.

We found also that the original inline fuel filter was removed at some point, even before we bought the engine. This filter was originally located after the fuel pump, aka, the gas running through it mixed already with the oil. We decided to add a fuel filter with water trap outside the engine, before the engine fuel inlet. Our added filter is now working with the gasoline only, but we concluded that the oil is very clean, and unless we do something really wrong and contaminate the oil tank, is not going to be an issue, and before anyway the engine was running without any filter!!!! well... it's a tough little merc... but we decided to give him a rest and at least some filtered gas... well, he's much happier now...

We have the same problem with oil flowing into the carbs on a 1996 4 cylinder 2 stroke Mercury. If we tilt the engine much the carbs seem to fill up with oil. We put a new oil check valve in and it still fills up in the carbs.
Now we are trying to leave the engine down and disconnecting the fuel line when not in use hoping that added pressure from a sun warmed tank won't push fuel into the engine.