Hi, I'm a french winemaker who worked 8 years in Napa CA.
Back in 1999, I bought a 1949 Cadillac, I restored it myself after getting lots of information from the right people at the right time. Now, it's back in France. It always ran very well until a few months ago when it started to smell gas, smoke black and also the ignition coil would get really hot. So I changed Distributor cap, rotor, condenser, plugs, wires plugs, points, gaz pump, and ignition coil...nothing changed. I am out of ideas. I took apart the carburator but everything looked ok.
I'm ready for any suggestion.

Thanks

Emmanuel

Do you have good compression in all 8 cylinders?

Black smoke, you have an over rich condition. Your carb is flooding or the choke is stuck. The gas smell confirms it. Keep looking towards the carb, maybe the choke isn't opening as the engine warms. wire the choke open and see if that makes a difference.

I think the compression is good but how can I check it ?
I am not a mechanic, more like a winemaker, but I learned a lot in the US. Here in France, we don't have big V8 and everything is now electronic, so it's hard to find a real good mechanic.
Is the choke the " trapp " on top of the carburator ?

Yes, although it's more commonly called the "butterfly". It closes off the air intake to the carb to create a richer mixture for cold conditions at startup.

One question: Does the black smoke occur all the time or only when you first start the car? My Buick did all of the things you describe when gasoline was reformulated in the U.S. to boil at a lower temperature in the late 1990s, except that the black smoke (very intense) only occurred for the first 30 seconds or so of driving. The heat from the engine at shut-off was boiling the gas in the (very small) carb, where is would either drip out the sides of the carb or down the carb throat. The gasoline odor was naturally overpowering. This created itensely rich conditions for a few minutes the next time it was run, until the car ran for a while and cleared it out. It was bad enough to foul plugs in 300-500 miles despite getting 13-17 mpg and running like a new car.

If your carburetor settings and functions are all O.K., this may be your problem. I was only able to correct it with an electric fuel pump and by relocating the fuel line away from the motor.

yes, the black smoke is mainly when I start and for about 10 mins when the car is warming up. I actually looked at the plugs and they are really black. I just received new ones but I know if I put the new ones in, they will be black too. What pisses me off is that this car always ran well since 1999, and I probably did something wrong one time and now, I can't adjust it. I need to readjust the butterfly then. The gas odor is terrible though, very strong. I also realized that the gas mileage was very low since that problem occured.
This car has been running in France since 2002 on unleaded gas without problems.

So, what should I do exactly ?

I actually forgot to say that the main problem is that when I accelerate, it's missing, like if the car had no power anymore. 1st and 2nd gear ok, and then when it's on 3rd and 4th, it doesnt run well.

It is hard to diagnose a problem from a distance, but I also keep thinking about the carburetor. I suspect that the float or the needle valve are not functioning properly inside the carburetor. Sometimes there could be dirt or a particle lodged between the needle and seat or the float is porous and is not at the correct level. You must remove the carburetor and check all of these possiblities.
Good Luck.
Joe, BCA 33493

when you say Needle, do you mean the 2 metering rods ?
I checked all this and it seems ok, but I will take it apart again and show it to a mechanic.
Thansks

No. Needle and seat refers to the two parts that make up the valve that lets fuel into the carburetor bowl. When closed, that is no fuel coming in, the needle fits into the seat and does not permit fuel to enter. The float tang or arm is connected to the needle. When the fuel in the carburetor drops, the needle moves away from the seat allowing fuel to flow from the fuel pump supply line. If thre is dirt on the space between the needle and seat it will stop the needle from closing off the fuel supply. If the float is porous it will sink and allow the needle to open and let in more fuel than is needed, leading to fuel smell and rich mixture.
Joe, BCA 33493

thanks for all your help but I did it all and it still doesnt run great. I don't get it. It starts perfectly fine, at idle, it's also perfect, and as soon as I accelerate, it's missing, it's not right.
I don't know what to do and I can't use this beautiful car. Too bad as it is finally sunny in France...

Any other suggestion would be great.

Thanks again.

Emmanuel

If the carburetor is in good condition and in tune, and you've checked all the other items above, perhaps double-checking the ignition system could be next? Black smoke indicates a rich mixture, but it may also indicate poor combustion. I noticed that you say your coil gets hot--do you have a spare you could use to check to see if that's the problem because there's no easy way to test a coil. They often work fine at low speeds, but under high demand situations, they start to break down and don't deliver full voltage.

Also double check the points and condenser, and make sure the timing is correct--too much retard could cause the smoke you describe and wouldn't be very noticable at idle. Since it only has problems under load and it misses badly, I'd check ignition next. It has to be fuel or ignition, and you've checked fuel.

Hope this helps.

Every poster has mentioned the choke. Black smoke is a rich mixture. The reason it performs poorly in high gear range is the load is too much for the engine. In lower gears, the higher rpms are moving more air through the engine - enough to at least keep it running. When the shift is made to a high gear, engine rpms go down, meaning less air movement through the engine and a mixture so rich, that the motor is misfiring.

There is no need to keep wondering what it is. Your options are: replace the carberator with a reman unit from a seller you trust (might take some back and forth with the States) or try installing a manual choke to override the automatic choke, which should be bi-metal.

I had a similar issue with many of my US cars, two in particular I never could get the parts I needed for the automatic choke so I installed a cable operated manual choke.

Manual chokes in my opinion - are superior to automatic chokes but in the interest of progress, most manufacturers went to automatic chokes.

On manual chokes, typically the choke is 'slammed' closed to start then pulled out almost immediately about half way, unless it's really cold out.

Then if the black smoke still keeps coming, you know it's an internal issue with the carberator, as your choke "butterfly" should be straight up and down - if you still get black smoke then, then I wouldn't mess around with it - send it to "The Carberator Shop" with a list of symptoms and he will rebuild it perfectly and send it to you.

Or get a remanufactured one. But this thread has seen a lot of "paralysis by analysis" but everyone seems to agree on the same 2-3 issues. So get on it and do it, then advise us.

Matt is absolutely right about poor combustion, and all of us have been analysing this problem from the perspective of poor air flow and/or excess fuel to the cylinder creating a rich mixture and thus black smoke. There is another way that poor combustion can be created in the cylinder that'll result in excess heat and poor combustion.

If indeed you have eliminated the carburetor as the source of the problem, and you're getting good spark, you may want to check your exhaust system. A blocked exhaust can easily cause these symptoms. Perhaps the manifold gasket is incorrect or incorrectly installed, partially blocking flow. It's unlikely, but there also could be a foreign object blocking flow inside the pipe or muffler.

If only the coil is getting hot it's probably true that Matt's correct and it should be replaced. You should have a weak spark if that's the case. If the coil is getting hot and the area around it is as well, you may have locallized a blockage in the exhaust system.

I'd replace the coil first (after checking the other ignition components of course), they're not very expensive. If that does it, you're home free.

I'm so lucky to be on this forum. Thanks for all the infos again, you guys are real pros.
What you have to know is that the coil has always been an issue for me. I've changed it 4 times and the last one comes from the US, 3 weeks ago, and it still gets really hot. When I say hot, it's actually burning, you can't touch it. That's one problem. But even when it got hot, the car would run ok. I actually installed a second one for a while and when it would get too hot, I would switch coil.
Now, the black smoke is mainly at the beginning, then after 5 mins, it's not black anymore, but it smells gas all over.
I also changed the points, the rotor, the condenser, the cap. Maybe the points are not adjusted correctly. And I touched at the advance too, still waiting for a timing light to adjust the all thing.Maybe that's the problem.

Finally, the choke might also be the problem, even if it looks like it's working fine, I need to see a professional about that.

Last infos, a friend of mine in CA is working on finding another carburator for me.

Thanks
You all deserve a nice glass of wine.

Emmanuel

It is rare to hear of an ignition coil that runs that hot. One cause might be a leaky condenser that still allows the car to run but draws excessive current through the coil. This might also explain the miss in the engine in the higher gears you describe. See if someone can check the condenser for leakage or replace with a known good one.
Any chance this car was converted to 12 volt battery system?
Joe, BCA 33493

yes, it is rare, but last owner, who is also my best friend in CA, keeps telling me it always been like that. Yes, this car was converted to a 12 V battery system.
Also, the condenser is brand new. It used to be one on top of the coil which I don't use anymore as a mechanic told me there was already one inside the distributor, near the points. I don't know what to do anymore, I checked everything. One last chance with another mechanic next week who told me it could be the choke...
I wish I would be in the US, my car would already be running for sure.
Back in 2000, I took all the wiring out and replaced it one wire at the time. I wonder if I did something wrong with the wiring going to the coil.
Anyway, thanks again for your infos, I'll keep you posted.

Emmanuel

Stupid question-you do have a 12v coil in it-if it has been converted to 12v?

The condenser mounted on the coil was almsot certainly there for AM radio interference suppression. Ignition condensers are almost always mounted inside the distributor, as you state.

If you disconnected/removed the radio suppression condenser it shouldn't have effected anything except AM radio reception, unless some of the other wiring was mounted to the original suppression condenser points instead of the correct location.

Maybe if you can post a photo of the coil someone could spot a problem?

If it has been converted to 12V, I have to ask, do you have a ballast resistor in the circuit to cut down the voltage to the coil? 12V coils are not designed to run on 12V's. The resistor cuts the voltage down to about 8V..! If you don't have the resistor, the coil will absolutely get hot..!

I would expect the car still has the 6v coil with 12v on it. A coil is a transformer-which consists of coils of wire wrapped around a steel core.

RocketDude:
Exactly why I asked if this car was converted to 12 volts! If he doesn't have a ballast resistor he is cooking the coil and burning the points.
I hope we find out what is going on here.
Joe, BCA 33493

well, the coil is a 12 v and the wire comes straight on it. There is no ballast resistor. The only ballast resistor that I use is for the cigar lighter and the gas gauge ( the gauge stoppped working anyway, but that's not an issue ). So I have to try wiring the coil via the ballast resistor and see if it stops getting hot.
Thanks everyone
I'm supposed to take the car to a professional mechanic tuesday. I'll keep you updated.

Emmanuel

I don't know what kind of resistor you are using on your lighter/gauges, but go to any parts store and buy a ballast resistor for the specific purpose of reducing the voltage to the coil in a 12V system.
They were used for years before they were replaced with calibrated resistance wire feeding the coil. They should be available even in France, if not, always mail order.... Cheap, too..!
Change your points while your at it, they are probably toasted. None of that stuff likes full 12V's..!
Good luck.... Let us know

As I think I understand the situation. You have a coil that is designed for 6v operation being used on 12v. That increases the voltage to the plugs about 2x. Which will kill the plugs. Which is probably the reason for black smoke??