Engine Idles ruff
 

I finally got my 58 Buick Special Running and it idles ruff. When I rev it up it seems to run fine. I do have some sputtering out of the tail pipe. I need help on what to check. I had the Gas tank cleaned, new fuel pump, carb rebuilt, timming set and new plugs point and condenser. what should I check next. Desperate. Big D

Could be a vacuum leak, but how did you set the point gap and plug gap also ?
You might have a bad plug wire, dist cap maybe even a cracked plug.
If the idle mixture screws on the carb are not right, too rich or too lean it could give you a rough idle.

Hanky,

I set the spark (new ones) gap at .032 the manual called for .030 - .035, I replaced the cap, rotor and points and I set the timming and set the points though with a feeler gauge. I am going to get a dwell meter and set it to 30 degrees. I set the two idle screws by backing them out about two turns. I did check for vacuum leak on carb and intake did find some of the bolts loose and tighened them. The exhuast does sputter at low idle and leaves a black mark on the floor. The engine sat for 10 years so that might b eexpected. Any other ideas Hanky.

Thanks

BIG D

Hanky,

I did notice that the Thermostatic Coil on manifold is missing. Will that cause a problem?

The butterfly inside where the coil is missing was to divert exhaust heat under the intake section to help vaporize the fuel when the engine was cold.
If you haven't adjusted the idle mixture screws they are adjusted by doing one at a time and turning the screw in until the engine falters then out until the engine idle speed is affected and placing the setting in the mid point of the range . Do that with both screws.
You need to make sure the choke blade is fully open when warm. I don't remember if the choke coil was electrically heated or if they used a tube from the exhaust manifold to get heat up to the choke coil.
This sure takes one back a bit !

Hanky,

Do I need to have the thermostatic coil in the manifold? Or should I just make sure it is open and wire in that position. With out this will it make the car run ruff? Do you think I should change the plug wire just to be safe? What would make the exhaust sputter when idleing? Thoughts?

Big D

If the sputter is consistent and regular it may be a cylinder misfiring. In that case you could short out each spark plug one at a time and you will get a double misfire until you get to the bad cylinder . At that time you will notice no difference when shorting out that plug. All that will do is tell you which cylinder has the problem which could be a bad wire, plug or something related to that particular cylinder like a valve problem.
If you take one step at a time you will be able to pin it down. Did you adjust the idle mixture screws as suggested ?

Hanky,

I did adjsut the idle mixture screws and it did not seem to help to much. I did spray some carb cleaner and that helped alittle bit. How do I short out the plugs for each cylinder. I am planning on changing the plug wire since they are not real expensive. I already just replaced the plugs again because they were really carboned up. Probably since the car sat for about 10 years without running. I am planning on putting some sea foam in the oil what do you think about that? Should I make sure that the thermostatic valve in the exhaust manifold is open that then wire it that way since I cant find a new coil for it.

Thanks, Big D

If I may,
The best thing you can do for the oil is , change it with a new filter.
If the car sat for any extended period of time some dry gas in the fuel tank might do more good.
Spark plugs can tell you a lot. When you removed them for the second time and they were full of carbon , that tells you the engine is getting extra fuel.
Either the choke is not opening all the way or the idle mixture screws are open too far or the carburetor is allowing too much fuel in. If one of the plugs was more carboned up and possibly wet that is the misfiring cylinder and it could be the wire that is defective.
To short out a plug when the engine is running , use a good insulated screwdriver with a wire connected to a good ground and the other end connected to the shaft of the screwdriver. Place the screwdriver next to the sparkplug boot on the plug and the spark should go to the screwdriver instead of to the plug. You will be providing a shortcut to ground and the cylinder should not fire and produce any power.

Many cars in those days drove around with the thermostatic butterfly frozen closed due to rust , so don't be too concerned with that right now.

Hanky,

Thanks and yes all of the plugs were really carboned up.. I have the idle screws about 2 to 2/12 turns out. I will check the choke. We did rebuild the carb and it seems to be okay? When we move the cam to fast idle on the carb it seems to run pretty good. When it heats up and drops off the fast idle cam then the car eventually goes to a lower and lower idle until the engine dies. I did replace the old vacuum hoses that I could find and also replaced the ones on the wipers since it uses vacuum.

Thanks,