black smoke on startup..Help

When I start the engine I get black smoke which goes away when the engine warms up. I pulled a plug and it’s full of black deposits. The plugs are new. Just had the carb rebuilt. Any ideas?
1985 Mercruiser 170 3.7L inline 4 engine

 

not really a petrol man, but sound like rich, rich means choke, auto choke ok?

 

Black smoke

Sounds like Lazeyjack is on the money. Check the choke - and check the air-filter, it's possibly blocked.

 

black smoke= fuel
blue smoke = oil
white smoke = steam
anything other color trouble
lazeyjack is on right path but if not choke you're still rich

 

the mixing screw is only out 1 1/2 turns. why do i still have a too rich mix?

 

ok disconnect your choke wire
lift thew air filter or wahtever you have on the carb
make sure the evnturis are open
start the motor and let it warm up tie the thing to a dock and put it in gear with a spring on
screw in the idle jet
til it runs rough
screw it out til it reaches max idle, , blip the throttle arm hard to make sure there are no flat spots
thats the easy part
make sure the cleats on deck are good) open the gas, little by littel , now screw the main jet in or out until the power increases
Now go buy me a bottle of Vodka)and some seeds for my parrot

 

and excuse the typos

 

if this does not cure it I spect the float level, you may then have to lower this
i dunno, how mechanical are you, I would hate for you to end up with needles and springs in the bilge
you could try google the make of carb, often there are pdf things to be found with exploded diagrammes and even stuff on overhaul
Petrol fuel her eis 5.50 an imperial gallon or 4.56 a US gal. Diesel is more

 

ya, i can get to the float w/ no problem. thanks will try all that and report back.
thanks for all the help

 

one more question...which is the idle jet screw and which is the main jet screw. i have the idel ajust screw w/ a spring and a long needle screw w/ a spring at the base of the carb.

 

you will find out at idle cos the main jet will not effect the idle sp. sorry I cant help on that

 

"Main Jet Screw"???

I would be surprised if that carb has a "Main Jet" or "High Speed Mixture" screw at all; most do not.

If you are seeing a screw with a spring around it, screwed into the carb body, that's likely the Idle Mixture adjustment.

A screw with a spring that is external and bears on an outside part is likely the idle speed adjustment.

If you start it cold with the air cleaner off, and hold the choke open you should not get black smoke. If you DO, then you probably need to look at the float level.

I once got a rebuilt Stromberg 97 Carburetor for my 1941 Ford. It ran really rough and black smoke. Found the 'rebuilt' float had a hole in it. That was only 51 years ago, but I'm sure it applies

 

Bollard Pull

Hello,

I see you have plenty of good advice. One comment I would throw in regards tying your boat up to a dock to put your engine under load. My recollection is that the technical name for this is a 'bollard pull.' However, dont just check the cleats - I suggest you check everything from your boat to planet earth. I remember one deserving fellow that drank too much one evening. When he climbed out from his boat the next morning, he found that he had a significant portion of a marina still tied to the stern of his 57' Chris Craft Constellation. It was part of the marina he was at the night before, and not the one he was tied to in the morning! Good Luck. John

 

If the engine runs/idles fine once warmed, it's probably the float valve and not the float level. Might be better after cleaning, but a new valve is cheap enough once you've spent the time. Vibration probably is necessary for it to seat completely. I doubt it's the choke. Also is probably running rich, a seperate problem, perhaps, or does it idle rough when warm?

Alan