Black smoke at first startup.

[thumpar]

This just started the last few times we have gone out. When it is first started after sitting for almost a week we get a few puffs of black smoke. I have to keep the throttle up to keep it running. It also sounds like it is missing for a minute or so. Once it smooths out it will idle fine. It runs great and starts easily all day after that. I have no problem spinning a 19 pitch prop at 4400 rpm so I am pretty sure the engine is fine. The rochester carb was rebuilt last season.

The thing I will note is that we just bought a new house. The begining of the driveway is at about a 20* angle. We park the boat on the trailer with the bow is up the driveway a bit so it sit bow up at about a 15* angle or maybe a tad more. Would this allow fuel to leak through the carb to cause a rich condition at the first startup after sitting? If can will it cause any damage?

Before going out the last 2 times I pulled the boat out to the street and started it up so that it is easy to start at the lake. Once there I just turn the key for a second and it starts right up. I let it warm up for a minute or so and we are good to go all day.

Boat info is in sig.

 

[Don S]

Re: Black smoke at first startup.

Check the automatic choke to see if it's working correctly. It sounds like typical choke operation on a carbed engine.

 

[thumpar]

Re: Black smoke at first startup.

The choke is working. It is odd that it just started doing this. Maybe I just never noticed it. My wife was the one that pointed it out.

 

[makonnen]

Re: Black smoke at first startup.

Black smoke = excessively rich mixture, as DonS said very likely the choke.

When you are cranking the engine, the choke should be near closed. The engine gets air and fuel from the ports right below the throttle plates. When your engine "catches" and starts, RPM increases, airflow increases. The increased airflow should crack onto the choke a little more. Notice that the choke plate linkage is not in the middle of the choke plate. Its offset, that way, airflow can open the choke a bit when engine starts. If the choke linkage / plate is sticky, this may not happen causing an over-rich mixture when the engine is started.

The obvious answer is to clean and lube the linkage, however I personally NEVER lube carb or throttle linkage UNLESS its with dry silicone lube. Any other wet lube, in my very humble opinion, would attract dust and dirt and eventually make things worse over time.

 

[Don S]

Re: Black smoke at first startup.

Air flow is not what opens a choke. The choke coil on the carb, the heat tube to the manifold is what opens the choke as the engine warms up.

 

[thumpar]

Re: Black smoke at first startup.

This has an electric choke.

 

[Grub54891]

Re: Black smoke at first startup.

You can "warm up" an electric choke, simply turn on the key,leave on for one minute.then start normally. Power will go to the choke,making it open up a bit before starting. If the black smoke goes away after this test,you need to service the choke.
Grub

 

[Don S]

Re: Black smoke at first startup.

This has an electric choke.

I guess I clicked on 82, not 83. Either way, if it only does it for a minute or so you probably just never noticed it before. It's very normal to have some black smoke when first starting and the choke is full on. As it opens, the smoke goes away.

 

[thumpar]

Re: Black smoke at first startup.

The thing that got me is that when we go out we run down the lake for about 45 minutes to our favorite spot and sit for hours. After 3 hours of sitting I would think the choke would cause the same thing but I don't have the same thing happen.

We only have 1 or 2, if we are lucky, days warm enough to go out this year. I will try the "warm up" on the next outing and see what happens.

 

[thumpar]

Re: Black smoke at first startup.

I guess I clicked on 82, not 83. Either way, if it only does it for a minute or so you probably just never noticed it before. It's very normal to have some black smoke when first starting and the choke is full on. As it opens, the smoke goes away.

OK. I just wanted to make sure it wouldn't cause damage. It only has smoke for a couple seconds. I take the family on long trips far from the launch and always want to be on top of taking care of this boat.

 

[Don S]

Re: Black smoke at first startup.

After 2 or 3 hours there is still warmth in the engine. Feel it. A warm engine will burn the excess fuel a lot better than a dead cold engine.

 

[makonnen]

Re: Black smoke at first startup.

You can "warm up" an electric choke, simply turn on the key,leave on for one minute.then start normally. Power will go to the choke,making it open up a bit before starting. If the black smoke goes away after this test,you need to service the choke.
Grub

Depends on how its wired. On a boat with electronic ignition (no points) and electric fuel pump ... the same circuit that powers the choke also powers the fuel pump, alternator field coils and ignition coil positive side. That circuit remains OFF unless (a) the engine is being cranked (b) the engine is running (ie: getting a signal from the cam sensor / reluctor wheel in the distributor).

So for instance on my boat, if you leave the key on, the choke (and the alternator field, ignition coil, fuel pump) remains unpowered until either the engine is running or its being cranked.

 

[makonnen]

Re: Black smoke at first startup.

Air flow is not what opens a choke. The choke coil on the carb, the heat tube to the manifold is what opens the choke as the engine warms up.

I'm going to have to respectfully disagree although I will say that I can't remember the last time I had to look at a choke that closely.

From my understanding, the rochester choke plate linkage is offset from the center for the same reason the air valves on a Quadrajet secondary circuit is offset from center. In a Qjet, airflow opens the secondary air valves. More airflow = more the secondary air valves open. Only when you crank the throttle 100%, there is a mechanical linkage that opens the Qjet air valves.

Same with a choke. The choke plate is offset so high airflow can open the choke. The electric coil opens the choke over a few minutes. However high airflow can open a choke faster than the elctric coil. If that didn't happen, the engine would spew black smoke if you revved the engine up while choke was still part closed.

And when you crank the throttle 100%, its probably because you're trying to clear a flooded condition so the choke has a mechanical linkage that opens it fully when throttle is opened fully.

Anyways I'm really curious about this, will need to check this out and maybe make a video.