Black smoke from original 305 engine in ’84 El Camino?

Question

My question is: what’s the likely cause and what’s the fix? I’m moderately handy with cars.

This is a car I purchased recently. (I have three other El’s, but have never seen this problem.) The car sat for three years before I got it. Seller said it had carburetor problems. 106k on the odometer.

Symptoms at present (persisting after some attempted fixes):

1. black smoke on start-up

2. black smoke while driving but at a lower level

3. more dense black smoke upon acceleration

4. misses upon start-up, then evens out


I have done the following:

a. replaced plugs; originals heavily carbonated

b. replaced distributor cap

c. changed oil

d. > > > swapped the carb from another 305 from an El that had been running well but has 238k < < <

e. treated the gasoline and added more new gasoline


Any advice will be GREATLY appreciated! Thanks for taking the time to respond!

Answer 1

Since you changed the carb... It might be bad timing... bad timing advance... vacuum lines leaking or in the wrong places... choke closed when it shouldn't be? Compression test might be a good idea to see if the engine's OK internally...

Did you replace the wires with the plugs? My brother had a boat where one (or more) of the wires was arcing to the block thtrough the insulation. It didn't create a "miss" or make a loud "zap", but there was smoke like it was running rich and the top speed was greatly effected. Took us a long time to figure out. The boat and wires were only 3 years old... The fact that your motor misses upon start up may point here.

I would make sure ALL the old gas is out of there before blaming anything else. Treating old, "dead" gas doesn't help much at all. Maybe replace the fuel filter after running the tank almost empty and filling 'er up. There's bound to be junk at the bottom of the tank.

Answer 2

Actual back smoke can be soot build up in the mufflers. But most the time it is good old rich running carburator. Quadra Jet 4 bbl carbs and dual jet carbs are notorious for float bowl leakage past the lead seals. But you have tried two carbs. What are the chances? 100 to 1. Install a new or rebuilt carb on her and blow out the exhaust a couple good acceleration runs. And see if you can spin a rod bearing. My el camino came with just such a problem major tune up got all the cyls running rebuilt the carb and the engine did not like it one bit KNOCK KNOCK KNOCK went the #5 rod bearing

Answer 3

The engine seems to be running too rich, but since you changed the carburetor, check the vacuum modulator valve on the automatic transmission. The valve will suck transmission fluid out of the transmission and through the vacuum hose to the engine if the diaphrams leaking. Also make sure the choke plate on the carburetor is fully open when the engine's hot.

Answer 4

Having black smoke comming out is usually because of carbon build up in the engine. My advice is this find a safe place that you can go full out with the car and put it to the floor, do that a few times and it should clean most of the carbon deposits out of the engine.

Answer 5

black smoke usually means you are running rich, be careful though cause if you are running too rich you may be thinning out your oil. I would replace the needle and seat and adjust the float.

Answer 6

You're burning oil. You probably need a rebuild.