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Lots of carbon out of the exhaust

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buick430

Regular Contributor
Hey guys, So today I started my boat after sitting for five days. When I started my stbd engine, it made two streams of what looked to be dried carbon for about thirty seconds. Prior to five day set I ran it for 25 miles at 3000RPM about 19 MPH. the engine ran fine and still does. What could be causing this? I dont have any chokes on either of the engines.

Thanks, will
 
It has no smoke at all to indicate burned oil. yes it only spits the carbon at initial start up after a long run AND sitting a few days. Oil level is holding steady and not fuel diluted. The engine in question has 970 hours. The other engine has 50 hours on it. When I rebuilt that engine I had both distributors professionally re-bushed and re curved. I will do a comp test tomorrow or the next day and post the results. I had thought about decarbing the older engine but haven't done it because it runs so well and has no problem making power, but come to think of, last fill up i dumped some STartron fuel additive/stabilizer. And no all the fuel in California has some amount of ethanol.
I'm trying to get a hold of a vacuum gauge to accurately adjust the mixture screws.

Thanks, will
 
Mine did that when I stupidly installed the raw water pump incorrectly, resulting in minimal water flow.

I strongly suggest you check your raw water pump impeller before it throws a vane into the motor.

Jeff
 
I checked the water pump today it was fine and discharge is equal to the port side. I also topped of the fuel tanks today and the stbd(one with lots of carbon) took ten more gallons than port. Im gonna pull the plugs tomorrow and do a comp check and try to see if its been running rich. Im still trying to find a vacuum gauge to adjust the carb.

thanks guys, will
 
I guess it could have been but it was all black with not even a hint of rust color. the manifolds and exhaust hoses are less than a year old. Im thinking im running rich on that side. Also the 10 gallon more consumption on that side has me a bit worried.

will
 
Okay so I pulled the plugs and tested compression as i thought they all tested good. 120-133. All my plugs were pretty black though. So I started it up and warmed it up. I tried adjusting the A/F screws and found the best quality idle at around 540* turns out. That is about 360* in from where it was set. Another thing I noticed, when I ran both screws all the way in, the engine continued to run when I thought it should have died. I am still running the carter AFB's. let me know what you think of this.

Will
 
Will .... a few suggestions.

buick430 said:
I guess it could have been but it was all black with not even a hint of rust color.
Iron oxide, when wet with water, may appear to look black.

the manifolds and exhaust hoses are less than a year old.
Is this engine fitted with a different make exhaust, and/or of different age?
Not all casting are made with the same quality..... and that may explain the rust scale... Key Word "may".

Im thinking im running rich on that side.
I agree with Kim...... swap carburetors, and see if the problem follows the carburetor.

Also the 10 gallon more consumption on that side has me a bit worried.
It is not uncommon for one engine to burn fuel at a different rate than the other..... but 10 GPH is excessive.
Click to expand...

buick430 said:
Okay so I pulled the plugs and tested compression as i thought they all tested good. 120-133. All my plugs were pretty black though. So I started it up and warmed it up. I tried adjusting the A/F screws and found the best quality idle at around 540* turns out. That is about 360* in from where it was set.
Remember that these control low speed fuel metering ONLY.

In order to change high speed fuel metering, (depending on the carburetor) we need to access the carburetor interior.

Another thing I noticed, when I ran both screws all the way in, the engine continued to run when I thought it should have died. I am still running the carter AFB's. let me know what you think of this.
If you closed off the low speed circuits, and if this engine continued to run OK, it's likely getting fuel from another area.
In which case Kim's carburetor float adjustment idea comes to mind.

Again..... swap carburetors.
The cost to swap them is two new base gaskets only, and a bit of your time.
Click to expand...

Also, have you given any thought to ignition timing?
NOT BASE advance, we're talking about the progressive advance, and the TA (total advance), and the RPM at which the advance occurs!
Many will set BASE advance, and will look no further.

Your progressive and TA are critical.




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I haven't swapped carbs yet, I am going to re adjust the float first. Does anyone know the specifications?

Rick, one of the first thing I checked was the TA. It still at 29* all in by 2950rpm

will
 
Will........
buick430 said:
I haven't swapped carbs yet, I am going to re adjust the float first. Does anyone know the specifications?
Which caburetors?

Rick, one of the first thing I checked was the TA. It still at 29* all in by 2950rpm
To date (unless someone has come up with this recently), no one has found a Chrysler Marine ignition advance curve that shows TA or at what RPM TA is to occur.

I'm not a Chrysler expert, but 29* full in by 2,950 rpm, would appear to be on the agressive side to me.
Click to expand...
I know that the 318/360 and 440 cylinder heads have what could be considered a "wedge" style chamber.
With any wedge style chamber, there is a quench surface. If the piston deck mirrors the quench surface, and if the quench dimension is tight, then you may get by with that advance number.




 
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This probably has nothing to do with Will's issue since he's confirmed that each engine is ignition timed the same.

I know that we're getting off topic here... so bear with me. :D

kimcrwbr1 said:
Again if the curve is the same as the other motor then that is where it needs to be. If I remember correct the chrysler curve is real aggressive and all in around 3000 rpms and WOT is 4000 rpms.
Click to expand...

Kim, I'd like to know just what the correct Chrysler Marine OEM Ignition Advance curve and TA are, relative to RPM?
I have never been able to see an actual Chrysler Marine Corp curve graph, and of the specs that I have seen, they just don't make any sense to me.

We all know that we don't dare use the automotive curves, and we are all familiar with Marine Load "detonation", and how destructive it can be.



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buick430 said:
good to see another thread that isn't at all timing related go that way once again! lol
Click to expand...
Well, I agree to a point.
The problem is, we often pay too little attention to ignition advance.

fastjeff said:
Rebuild that carb--don't waste your time switching them. THen go boating!
Click to expand...
Jeff, while I certainly agree with you that this carburetor may be in need of an over-haul, if he swaps carburetors, and finds that the problem remained with the Stbd engine, then his issue is elsewhere.

This would be a P of E that he could use to his advantage.

Just say'n.


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fastjeff said:
If the wind knocks you over, you don't have to measure it to see if it was a high wind!
Click to expand...
Jeff, that is certainly true.
But what if the possibilities were high wind, a slippery surface, gravity, being off-balance, etc?

Like said.... this carburetor could be in need of an over-haul....... but for the cost of two new base gaskets, he can either prove or disprove this theory.
One carburetor would be coming off anyway.

I'm not arguing with you..... just making a suggestion.



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