Black substabce in water

"This may sound like a dumb qu

"This may sound like a dumb question but since I am new to owning an I/O, I need to ask. I noticed today, that my boat, (which has a 120HP Mercruiser) when it is going slow or at idle, leaves a black substance behind it in the water. Now, I'd have to guess that it's oil but my question would be if this is normal? It also seems to smoke a tiny bit at idle. I just want to make sure if this is normal things to see when running these or if something is wrong again...

Thank you again "

Check the choke. Sounds as if

Check the choke. Sounds as if it is running rich. The black is from the exhuast. It should not be oil. If it is oil you had better find out where it came from. Boats do not leak oil if all seals are good.

"Okay, oil might not have been

"Okay, oil might not have been an accurate guess

When you say "check the choke", what am I looking for? If running rich, how is this corrected?

Thanks for the reply Not Me!!"

"Lee-
How old is your boat?

"Lee-
How old is your boat? I have a 76 imperial with a 120hp, with an automatic choke. It is round, and has an air line coming from the maifold. on it there is a flat slot in the center, which can be turned to adjust the rich/lean running. start there. the idea of the auto choke is to keep the choke closed when the motor is cold, and as warm air from the manifold heats the auto choke it opens the choke further.
Good luck
Jeff"

Mine's an '85 and I be

Mine's an '85 and I believe I remember seeing a choke similar to what you described. I'll take a look at it today as I'll have it out on the water.

Greatly appreciated!!

"When the boat is warm, take o

"When the boat is warm, take off the flame arrestor (air filter lookn thing) and look at the top butterfly valve, it should be straight up and down to allow the most air in."

"Since the flame arrestor is c

"Since the flame arrestor is coming off, clean it. This is the #1 thing I have seen neglected by boat owners and I have "fixed" boats that ran like crap, just by doing this.

If it can't breathe, it won't run right and will leave a trail like a snail."

"Took it out this morning, and

"Took it out this morning, and I had a look at the carb. There is a "round thing" on the front of the carb that the guy at the shop told me was the choke. It has 3 screws that appear to hold the front piece in place. Looked like if I loosened these 3 screws, that it turned, maybe to adjust the lean/rich. So, I gave it a very small turn. The boat doesn't seem to smoke as much now and also doesn't leave as much "exhaust" on the water now. So, guess I was going in the right direction, just maybe need to go a bit more.

This "flame arrestor" I assume is the thing sitting on top of the carb, like said, looks like an air filter. I should be able to just blast this thing with the air compressor to clean it?

You guys in here are great, huge help!!"

"OK, now that you have the [i]

"OK, now that you have the choke thermostat misadjusted, you need to make sure it goes to the right position when the motor is cold. IIRC, the choke plate should have a 3/16" gap at this time. The choke is only for running cold and should do little or nothing (possibly closing slightly under hard acceleration to get more gas into the intake) when the motor is at normal operating temperature. If the choke thermostat is reset to factory spec and it still runs rich, the carb needs to be readjusted or rebuilt.

Use carb cleaner for the flame arrestor, then blow it out. I like the NAPA stuff in the blue can because it doesn't waste time dissolving the stuff on the arrestor. If it's hot and humid, you'll see frost form because it evaporates so fast. Just wipe it off and put it back on."

"choke thermostat?? Hmmm. Goo

"choke thermostat?? Hmmm. Good thing I marked where it was before I moved it, even though I moved it ever so slightly. Since I had the wrong thing, where is the rich adjustment? According to the guy at the shop, the carb on this thing has been rebuilt just recently and it ran fine before I had this "water in the gas" incident. This guy said he cleaned the carb for water and now it runs like this."

"If there's still water in

"If there's still water in the gas, it could be that you need to get rid of the water before doing anything else. The mixture adjestment is usually at the front of the carb base. If it's a 4BBL, there will be two of them."

Lee.
Did the person working

Lee.
Did the person working on the carb know what they were doing? Just what did they do to the carb? (take it apart or just dump the water out of it etc.) If they took it apart did they install new gaskets? This can be a concern.
Depending on the type and model of carb you have there is very little that can be done to change how rich or lean it runs.
This is controled by the main jets except for the idle. Main jets are fixed and can only be change by installing bigger or smaller jets.
The idle mixture can be change by the idle mixture screw / screws at the base of the carb. These should be about 1.5 turns out from closed.

If the choke is not opening the engine will run very rich.
The round part on the side of the carb with 3 screws controls the choke.
This black part should be marked with rich / lean with arrows pointing the direction to move it. Rich the choke is closed longer / lean it opens faster. A boat does not need a lot of choke time since it is run during warmer times of the year. So you want it to open fast.
I've fixed mine so they do not even close. They are really not needed. Anyway to adjust it. With the engine cold open the throttle a little to release the choke.
Move the round black part until the choke is just about in the full closed position.
Then move it back until the choke just starts to open.
Do not make a full turn.
Tighten the screws and start the engine.
The choke should open about half way when the engine starts.
This you may need to fine tune for correct operation.
The choke should continue to open as the engine warms up.
When the engine is at operating temp the choke needs to be full opened.
If everyting is correct in the carburetor this should fix the problem.
Good luck.

"Hey Not Me

I would like t

"Hey Not Me

I would like to assume that this guy knew what he was doing. He's been in business in my area for many years, and although I know this is no gaurantee that he "knows", I sure hope so. Anyway, I believe all he did was clean the carb out and not rebuild it.

I'll look more into the carb tomorrow. Thanks for all the info!"