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dark colored exhaust question


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I am looking for some insight on dark ciolored exhaust. I understand it can be that the car is burning oil due to a need for new valve rings (I believe) is that the only thing that can cause it or could it be something else. Let me fill you in on my car which may help with the advice.

I found my car on a ranch beneath a car port this last winter. It is a a 1971 with the original engine which has 131,000 miles on it. It was last driven in 1987 when it started sitting in a garage when the owner bought a new car. It was moved to the ranch I found it on (my neighbor's) about 5 years ago or so. I brought it home and with little effort got it running. The choke was frozen at half open but the car seemed to run fine. After it warmed up no color in the exhaust. Well I spent the last few months cleaning it up and doing other things and did not mess with the engine much.

I recently added new performance plugs, wires, petronix ignition with the flame thrower coil, fixed the choke, new filters, thermostat distibuter cap, rotor. The car starts right up, when it is warmed up it idles at 750 rpm which I believe is the correct speed. When I rev it it sounds smooth and strong except it starts to put out a dark colored exhaust once the rpm get above a couple thousand or so. Also it will backfire at the intake at the begining of the rev on occasion (seems like it does then when I rev it rapidly).

I am thinking I probably will have to replace the valve rings, but could this dark colored exhaust be caused because the car has bot been driven in so long, or could the carbs need adjusting? I have seen those additives that claim they will stop smoking is this something I should look into? I am just looking for a little advice and insight on what could be or probably is going on with my car. As soon as I finish the brakes which should be in the next week or so I will get the car on the road and maybe learn a little more.

Thank you in advance.

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Bart, there is no such thing as valve rings. Valve seats, valve seals, valve guides perhaps, but no rings. Rings generally refer to piston rings.

Now, exhaust smoke can be black and it can be blue-grey-white. Black, sooty smoke is too rich a fuel mixture and your carbs need work. Blue-grey-white is burning oil and you have engine problems.

Do a compression test on your cylinders to determine if you have piston ring problems. You should get even compression numbers from all six cylinders. Squirt some oil in a low compression cylinder and if the compression jumps way up, its piston rings. If the compression reading stays about the same (with blue-grey-white smoke), suspect the valve train and do a valve job.

Your explanation of back-firing sounds like carburation and fuel delivery. I assume you set the timing correctly from your description of ignition work, but bad timing will cause a backfire.

Check your spark plugs after running the car and shutting it off from steady revs of 2500 or more. Are they oil fouled or black and sooty? Spark plugs should look light brown. Oil fouled plugs will look oily and grimey. Fuel fouled plugs will look black and sooty.

After sitting for such a time, the car may have a number of problems, but from your description, I would thoroughly clean, tune and sync the carbs. Finally, make sure the timing is correct.

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