Soot from exhaust on start-up

grumppyoldman

grumppyoldman

Well-known member
Since I've started using non-ethenol gas I've noticed soot comes out of both tail pipes when engine is fired-up. This is after setting for a month or more. At first I thought it was oil, but it's dry soot and droplets of water. The water I understand, it's just a few drops of clear moisture ( condensate from high humidity collecting in mufflers ) but don't know what the reason's for the soot. engine don't smoke and don't use oil. The car had been sitting for a while before I bought it. Al
 
It could be as simple as the choke mechanism being set too rich (or stuck).
Which carburetor does the car have?

Or,
the carb maybe letting too much gas thru and the engine is running rich all the time. The tailpipe(s) will have black soot inside and the center insulator of the spark plugs will be black as well.
Depending on how long the car sat before you bought it, the carb may need gaskets & internal rubber parts.

Scicala is a very good carb person on this forum.

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I (think) I have a similar issue if by dry smoke you mean whitish? Also my tailpipes easily get black soot on the outside chromed areas (within in just one or two drives after cleaning the chrome). I haven't checked the plugs but is this a sign my engine running rich? If so how do I confirm the engine is running rich, and then how do I confirm that's due to the carb?
 
I've read plugs for years, but trying to do it with ethanol fuel seems more difficult. They all seem to run pretty light even with proper jetting off the dyno. But remember back in the day, a bit or black smoke on start up wasn't uncommon. The choke could be fully closed before the vacuum signal from a running engine pulled it off a bit. Likewise running down hill with the throttle closed made many go rich-remember the burble in the exhaust that went away when EFI started shutting the fuel off on trailing throttle? So you might be fine, and it's just the way it used to be.
 
My carb. is a Weber 4 barrel, on an Edlebrock manifold. it has a manual choke. I've seen black smoke on start-up when valve stem seals were bad, but there is no smoke. Just soot on the floor, I've thought about trickling water through carb. keeping engine running to see if the steam would remove it from exhaust system. All exhaust system is new, anymore thoughts. The carb. has been rebuilt and set with vacuum gauge. Al
 
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The replacement 4bbl carburetor on my '55 292 was rebuilt by a well rated local shop and was supposed to have smaller main jets suitable for the elevation here (5200 ft).
The exhaust always smelled rich and the tailpipes were coated inside with black soot that spit out on the garage floor when starting. I pulled the main jets out and discovered they were 4+ sizes larger than recommended in the shop manual chart.
'Rebuilt' doesn't mean it's right.

Another topic? Is the distributor oem for '55 (a Loadomatic) or something else?
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dmsfrr said:
The replacement 4bbl carburetor on my '55 292 was rebuilt by a well rated local shop and was supposed to have smaller main jets suitable for the elevation here (5200 ft).

The exhaust smelled rich and the tailpipes were coated inside with black soot that spit out on the floor when starting. I pulled the main jets out and discovered they were 4+ sizes larger than recommended in the shop manual chart.

'Rebuilt' doesn't mean it's right.
Click to expand...

No truer words have been said.

The SPECS for the carb are included in the SM. You start there and go from there. If it is showing soot, it is a too rich mixture for whatever reason(s). Without a exhaust gas analyzer, it is a guessing game.
 
i'm at sea level and the jets could be the problem because the car came from Arizona. I'll have to check that out, maybe smaller jets will help. The no-ethenol gas is 92 octane and that could have some effect also. Al
 
Black soot cam accumulate in the exhaust system from cold starts with the choke on even when correctly adjusted sometimes. It takes a long time for the black to change colors once it's there. With condensation in the exhaust system, sometimes the soot spits out with the water. To me it's kind of normal. You know, the good old days.
Also, I have heard the Edelbrock carbs come new on the rich side, but haven't experienced it myself.


Sal
 
My avatar 302 also does the soot on the floor thing until it warms up enough for the auto choke to open then no more soot. Choke of course makes it run rich.
 
Don't forget IGNITION. If not par, a weaK spark can cause incomplete combustion, especially on an old points system with GEN.
 
grumppyoldman said:
i'm at sea level and the jets could be the problem because the car came from Arizona. I'll have to check that out, maybe smaller jets will help. The no-ethenol gas is 92 octane and that could have some effect also. Al
Click to expand...

Depending on what part of Arizona the car came from, it may already have smaller jets. The higher the altitude, the smaller the jet size needed, and much of Arizona is mountainous. Phoenix is only around 1200 ft., but Tucson is about 3,000 ft., where jet size may need to reduced, Sedona around 5,000 ft. and Flagstaff is at 7,000 ft., for example.
In addition, if the car were jetted for using ethanol fuel at lower elevations, it will have larger jets. This is because ethanol is an "oxygenated fuel", that is, it releases oxygen when burned which has the effect of leaning out the mixture. Going back to non-ethanol fuel will mean jetting down, to smaller jets to avoid running too rich.
Finally, if the idle mixture screws were set with a vacuum gauge, it is almost certainly set too rich! Here is what I was taught when becoming a licensed emissions inspector to get older carbureted cars to pass (all you need is a tachometer): With the engine idling at operating temperature, first adjust each mixture screw to get the highest RPM, then reset idle RPM to factory specs. Recheck mixture screws and idle RPM if necessary. Then turn one mixture screw in (lean) to drop idle speed about 25 RPM. Do the same with the other screw, dropping another 25 RPM. This is referred to as "lean best idle" and will not only help pass emissions but give better mileage around town and stop washing down your cylinders from a too rich mixture.

A vacuum gauge is NOT a tune-up instrument! It is a diagnostic tool, for finding problems like a burned valve, leaking intake gaskets, or worn timing chain. Vacuum readings are not precise enough to set idle mixture nor ignition timing! That is just so primitive! It's not that hard to use a tachometer and a timing light. Don't blow dollars out the tailpipe!
 
a vacuum gauge is not a tune-up instrument! It is a diagnostic tool, for finding problems like a burned valve, leaking intake gaskets, or worn timing chain.

Vacuum readings are not precise enough to set idle mixture nor ignition timing! That is just so primitive! It's not that hard to use a tachometer and a timing light. Don't blow dollars out the tailpipe!
Click to expand...




!!! Good advice there !!!
 
Try taking it for a 100 mile drive. If the car is never "heat soaked" the normal carbon build from cold start will never be cleaned out of the exhaust system. After the 100 mile trip let it cool and sit overnight and see if the same thing happens.
 
Respectfully I disagree with having to go to different sized main jets when using 10% ethanol fuel.


Sal
 
Mine only started when I started using no-ethenol gas, the engine runs better in both my cars. My 55 Fairlane and 41 Ford flathead V8, the flathead hasn't had any soot at all. I've driven both around 20 to 30 miles each time I take them out. Don't know whyy the flathead doesn't soot like the 302. Al
 
grumppyoldman said:
Mine only started when I started using no-ethenol gas, the engine runs better in both my cars. My 55 Fairlane and 41 Ford flathead V8, the flathead hasn't had any soot at all. I've driven both around 20 to 30 miles each time I take them out. Don't know whyy the flathead doesn't soot like the 302. Al
Click to expand...
So your '55 Fairlane doesn't have the original Y-block, it's a 302...
It's because the '41 flathead has a carb that isn't passing too much fuel. ;)
I like to set the choke mechanism toward the Lean side of the adjustment, just enough so it starts without much trouble. And having a light to medium brown color on the sparkplug insulators.
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scicala said:
Respectfully I disagree with having to go to different sized main jets when using 10% ethanol fuel.


Sal
Click to expand...

That's usually because cars of the pre-emissions era ran on the rich side, especially after some miles and wear on them. A main reason ethanol was mandated was to lean an engine down without any carb adjustments nor re-jetting. Since ethanol releases oxygen when it burns, the result is a leaner mixture thus lower emissions. Back when smog equipment first came on new cars, this was a quick easy way to get older cars to pollute less. If you had already fine tuned your carb jets for economy, often times using 10% ethanol was enough to cause a lean misfire.
You may remember those air cleaners with the tubes leading to a shroud around the exhaust manifold. This supplied hot air to the carb to better vaporize the fuel so the car would run OK with the leaner mixtures.

The "benefits" of ethanol went away with the advent of computer controlled carbs and electronic fuel injection. This is because the oxygen sensor senses the extra oxygen released from the ethanol. Since the computer is programmed to maintain a 14.7 to 1 fuel ratio, it richens the mixture to maintain that ratio, thus using a bit more fuel than with pure gasoline. My Honda CR-V gets about 2-3 more MPG on pure gasoline than 10% ethanol (pumps usually say "at least 10% ethanol"). This is because of tax breaks on ethanol. It's cheaper (or at least was) for refineries to add a little extra ethanol to reduce costs.
 
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This period engine used a hot air only (auto) choke assy. If the cylinders are sooted (for whatever reason), the hot air choke system will also be sooted leading to an inoperative choke. It it freezes on the enriched position, it will only compound the problems(s).

It may also be a good idea to take it out on INTERSTATE and blow her out from time to time. Carburetion is a long forgotten art.
 
Started the 55 up today, no soot, I guess running the crap out of it the day before cleared it out. So I poured a little water through carb. and blew some more soot out, It should be cleared out now. Al
 
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