40 Plymouth Not running "clean"

[Don St Peter]

I have been driving my car ( original engine) quite a bit and keep noticing a significant amount of black soot ( carbon I suspect ) on the driveway at the tail pipe. The engine is running smooth, no smoking, little oil usage, but its beginning to worry me because the soot persists and the oil is a very dirty black, even though it has less than 200 miles since oil change. The car is making about 11 miles/gal and I suspect it should be doing much better. The plugs are also showing evidence of "dirty" combustion with some carbon build up. The car seems to be OK on power, but I have not yet checked compression. Since replacing the head gasket, I have been burning regular unleaded gasoline. Should I be adding a lead additive? Does anyone have suggestions as to the problem and possible things to do first.... like adding a bit of diesel fuel to the gas tank, other gas/oil additive, something thru the carb. etc.

Thanks in Advance

Don

[Guest Nelsons Ply]

Don

My car has 77000 plus mileson the motor.Tail pipe is always black But I get about 14.5 miles per gal.

It is due for rebuild But the car still runs great.

And my oil is always black and it also uses a lot of oil but very little smoke.When i back off it puffs out some but not much.

If I were you I woul reset the carb sounds like you may be to rich.

Look at the dip stick and see it has bubbles on it.

Gas in the oil will a sooty tail pipe.

If you set the carb idel about 450to500 rpms turn the mixture until the motor stumbles then back off1/4 turn or until it smooths out.

Hope you get it running the way you wont.

Oh And another thing blow the soot out once in a while.

Go up to 60 or so let off back to 40 or so then do that two or three times.I push mine pretty hard often.

[greg g]

Several things to look at. Make sure that your choke is fully opened at normal operating positon. Make sure you float level is set correctly, does the oil smell like it has gas in it??? What spark plugs are you running? Make sure your spark plug wires are fully seated in the distribuor cap. Push them in real good. Is your vacuum advance working correctly?? Have you done a compression test. What are you running for an air cleaner? Depending on how and where your are driving, you should be getting a bit better gas milage. Questions every now and again on this board usually have a consensus of 15 to 19 with overdirve equiped cars getting in the low to mid 20's. 11 seems low. Our old flatheads were blessed with hardened valve seats and running lead replacement adiditves is not necessary.

Where is your timing set?? Do a road timing session with your car and see if it makes a difference. To do this, loosen the distributor hold down so you can turn the dizzy but it still has some resistance to turning. Crank in a little advance (counter clockwise) and drive the car, accelerating smartly or climbing hills with wide open throttle. Continue to advance the disributor till you hear the engine begine to ping or knock. Then back the dizzy off a couple of degrees till the knock disappears and lock it down. If you encounter hard starting with a hot engine back it off a little more. Run it this way and chack your plugs.

[grey beard]

That black soot on your driveway is an indication your engine is running very rich. Your fuel economy bears this theory out. Things that make engines run rich:

Choke partly closed

Timing retarded

Air cleaner partially plugged

Heat riser valve stuck in the "closed" or counter clockwise position

Thermostat stuck open - engine not coming up to operating temperature

First thing I woudl suggest is to remove the air cleaner and look to see if the choke plate is really open completely - standing vertically - when the dash knob is pushed in the whole way. Your problem may be as simple as a cable adjustment. Next, while it's off, check the air cleaner to be sure it does not need servicing.

Your black oil sounds like it may be the result of someone in the lifetime of the vehicle switching to detergent oil on an older engine with years of accumulated dirt in the crankcase. This is not normal for healthy flatheads. Do you change the filter with each oil change? How does that look when it comes out? Another concern here is that the engine may be running so rich that fuel is contaminating your engine oil - not a good thing for your engine. This is why the other guys asked how your oil smells - if it smells of gasoline, I'd find the problem before driving it very far.

My bet is that once you find the "too rich" problem at idle, your fuel ecohomy will show a healthy gain. You may even see the following oil change stay clean longer, too.

LOL

[De Soto Frank]

Another thought...

You're "driving it a lot" ? A lot of short trips ( 5 miles or less), or does it get a good run at 40 MPH or more for 15-20 minutes or more ?

Any internal combustion vehicle needs to be operated at normal operating temps for at least 15 minutes, to get the oil hot and to burn-off carbon, cranckase dilution, etc....

There is some sound science behind the notion of taking the car out on the highway once a week to "blow the carbon out"; that doesn't have to mean trying to "burn rubber" or set a new land speed record; just drive it at a good clip for 10-15 miles to burn all the crud out...

If you car has an oil-bath air cleaner, make sure the element is clean and that the correct oil & level are being maintained.

I would agree that 11 MPG is below average for a six-cylinder MoPar...

Greybeard made a good checklist...

[Don St Peter]

Thanks to all for the great info and suggestions. I have followed up on some of them and I'm on my way to complete the rest. No one mentioned my worst fears, like burnt or stuck valves so I persued the easy ones first with the following findings.

1. I recently overhauled the Carb. and set float level etc. I do notice that the choke connector rod seems to have quite a "free play" and seems to hold the choke butterfly about 5 degrees from full open. This would probably account for the fact I can not get the engine to idle down most of the time without "gunning" the engine then let it back down on it's own. When it does idle down ( sometimes) it seems about right. I also cannot seem to find an adjustment for this on the throttle shaft lever end. Also, I was wondering if the choke spring might be bad by not pulling the choke fully open. From what I'm hearing from you guys this butterfly issue could be my total problem. Do any of you know of an adjustment to get the choke butterfly to stay full open when the choke cable is full "in" at the dash control?

2. There is no fuel in the oil.

3. The plug wires are all new and in good contact with the distributor and AC spark plugs adjusted to .025.

4. The air cleaner is original metal material which I clean with gasoline occassionally. I keep clean oil in the cleaner and do not operate in much dust.

5. I am interested in the "road timing" session mentioned by Greg for checking timing, but I seem to not be able to comprehend the concept, probably because I don't know the terms like "dizzy" and "crank in a little advance" etc. Can I loosen and turn the distributor with the engine running? I'm sorry for showing my ignorance here. Can you help me out here?

I am going to get some help running the compression test. Can someone give me an acceptable range for my old engine?

Again thanks to all

Don

[Guest Nelsons Ply]

Don

You say it idles down sometime.Check the return spring on the foot pedal.put more tension on the spring.

Next time you start the car.if it is idleing to fast see if you can pull back on the pedal .

Like some said it my be a linkage problem.

[Don G 1947]

Don,

I'm sure I speak for all of us on this board. We are all here to learn from each other through asking questions. I've asked some pretty simple questions in my time and have always received helpful and courteous replies. Don't ever hesitate to ask what you may think is a simple question because there are probably several others of us out there that have wondered the same thing. I'm sure some great, often quoted person from the past has said, "The only dumb question is the one that isn't asked." If it hasn't been said in the past then you heard it here first, and you can quote me anytime!

I learned a lot from the replies to your question and have printed several of them to include in a notebook I keep on tips and valuable information.

Don

[Guest Roadrunner]

What he was referring as a "dizzy" is the distributor. You loosen the distrutor a little so you can turn it but it still has tension. Drive the car down the street and every few miles advance the timing. (turning the Dist. against the dirrection of the rotor spinning) this is advancing. It makes the spark sooner. When you advance it to far as you drive it will "ping" or what also is called "spark knock" It won't hurt the car for a little while. When it pings, retard the timing a little bit until it goes away. Then lock down your Dist. You will be opening and closing your hood quite a few times during this procedure. I have done this on a few vehicles. It works every time.

Hope this helps. As somebody else said, Don't be afraid to ask.

[Guest Roadrunner]

Oh, My girlfriend and I also have a 1940 Plymouth. It is a 4 door in bad shape but we will get started on her soon

This is one of the only photos we have of the little Mopar. She's in the shop now and looking better but is still in the same shape for now. What shape was your's in when you got her. This one is all there just been forgotten about. The other pics I posted are under the thread Attempt topost a pis and more 1940 pics.

[Don St Peter]

Roadrunner:

Thanks for the pic and the "dizzy" explaination. I tried posting a before and after of my 40 but image exceeded posting limit. Looks like you have a project car there!

Thanks

Don

[Guest Roadrunner]

I learned how to use another site called Photobucket.com I was able to resize the pictures there. Upload them to there and resize them. then you can post them to the URL spot when you click on the envelope with the mountains on it. Use the Cut and Paste using your right click. That is how I did it.

[greg g]

Sorry I confused you with the shadetree shorthand. And yes you can run the engine with the distributor loose. Just not too loose. Roadrunner's explaination was right on. loosen the hold down screw till you can turn the dist against some slight resistance, and leave it loose as you adjust it. You can move it while the car is idling, but you need to put the road load on it to affect the proper setting. By road load I mean, briskly accelerating or climbing a moderate hill under wide open throttle. Then yo listen for the ping, spark knock, and repeat as necessary to induce the knock with advance and then get rid of it with small amount of retard till it goes away. Kinda makes you wish that the manufacturers had never taken the spark control levers off the steering wheel hub........

[Guest Roadrunner]

I just got done doing that on Darrien's 80 Truck witha 425 CID Caddy in it. Took me 4 shots opening and closing the hood to get her PERFECT:D

Long story here.