what causes black smoke on rev up

got a quadra jet carb on my truck seams to run ok but on rev up it blows black smoke. is it running to fat or lean. how should i adjust it. thanks

 

Black smoke is rich.

What exactly is " a rev up"?

 

too rich, usually accelerator pump, but hard to "adjust" on a qjet........may have to live with it if its not too bad...

 

Too rich,it can be too rich from many things,The two most comman are high fuel in float bowl or your trying to use a carb that is too big for the motor size

 

thanks guys its on a 350 . and rev up i mean give it some gas in park.

 

Ok, your rev up is gas in park -
on a cold engine not yet up to operating temp,
that's sort of normal since the choke is partially closed. Also not a good idea to rev a cold engine, lots if bad things happen. The choke plate restricts air flow, when you give it gas the accelerator pump squirts fuel co compensate for the throttle blades opening until the jets work off of bernoulis principal. The choke plate hampers that. There should be a fast idle cam on the carb, let it do its job.

On an engine that's warm, gas in park - why?
There's probably some malfunction in the carb, but again why rev it up ?

How's the drivability? Does it bog, cough, flat spot, or any other thing ? Blow black smoke on the highway? Do the blugs look dark and sooty ?

 

Is this something that just started, or a long time (since fresh) condition?

 

How about you start with the basic's, and the fact that 95 percent of the time the carb is blamed and it's well- not the carb.
Basic's would be some more presise info, as in has anything been changed, and did this just start recently, did you just get the car/truck?
Have you pulled the spark plugs and checked them, when is the last tune up?
Could be something very simple or fairly serious, please give some more details and backround, if not we are just stabbing here, TR

 

You have approximately a 95 percent probability that the carb is NOT the culprit.

Check out the compression and ignition FIRST .

If the carb is the culprit, the two most common items which would cause black smoke when revving the engine are:

(1) if the idle mixture control screws are set too rich, and the throttle positioner screw is too far out, the intake manifold will "load up" (droplets of fuel will adhere to the runners in the intake manifold); and when the throttle is opened, all of this excess fuel will be swept into the engine, creating a very rich condition and black smoke.

(2) a defective (fuel soaked) float.

A more detailed question would precipitate a more well-informed answer.

Jon.

 

Man I love the HAMB.

 

The black smoke is for decorating the doors, isn't it?

 

Nope! Communication when you get "no signal" on your cell phone.

Jon.

 

Ah cheer up! I had a brand new one and it did the same thing. Chevy people told me nothing was wrong with it. And I took it to more than one dealership too. After the warantee ran out, I pulled it and put on a Holley. Mucho better. I have read that there is a place on the underside that can and will leak fuel under the right conditions. The fix is to epoxy over a plugged section. But mine blew black smoke every time you got on it, hot, or cold, made no difference. HEI was perfect too. They checked that out several times.

 

The last qjet I put a kit in (after a good soak of course), the owner complained of black smoke on accel. I couldn't see it. I told him to show me. He was FLOORING the pedal in park. Black smoke is then to be expected! If you get smoke with "normal" take-off then you have a float issue or weak needle. This stupid ethanol is wreaking havoc on needles. You would also be fouling a plug or 3. peace