When ever the vehical takes off, it puts out a little black smoke. While as I'm not throwing a fit, my dad who I built the engine for is.... He keeps leaning the mixture to where it runs nice at idle, but dies on it's face when you try to take off.

Could this be a problem with the jet sizing? I don't really know.

I do know that when you take off there is no splash shield with a normal SBC pan, and the 383 rotating assembly wips some oil up and it burns some. (when the engine gets put into another vehical this will be fixed and replaced)

Any suggestions? Tuning this thing seems never ending, a vacuum gauage tuning session doesn't yield an anwser either way...

details please. Carb type. Condition. Do you still get the black smoke when it "falls on it's face." Any oil burning will be blue/white. What do your plugs look like under different test drive conditions. The pros here can help if they know some of this stuff.
Darryl

It's a Speed Demon mechanical seconday. (pretty new, engine was built last year, Demon bought months after)

It doesn't fall on it's face. Yes the oil is white smoke, you can see that.

I'm sure the plugs are getting to a smooth black. The engine has almost 11:1 compression, it's like 10.6-10.9 area. (spark plugs gapped to 47)

Could the secondaries be opening to fast, or is the black smoke just to rich ? I put a different power valve in it, could open TO fast? Stock powervalve wouldn't work with operating readings of vacuum hg, I think it has a 4.5hg or what ever was close to that. The stock was like 8hg or some thing, this one right at 2-3hg below the engine in gear with brake on at idle.

[This message has been edited by GoodToTheTouch (edited August 27, 2005).]

The black smoke at accelleration is probrably to large accel pump discharge or power valve opening to fast? If its falling on its face its either power valve opening too slow or late accel pump shot.

It doesn't fall on it's face, if you press on the gas the engine responds faster then any new vehical and most old ones.... It has like 10-14 initial timing.

However it does take the engine a moment to rev up to where the torque converter will grab.

Why did you tell us " but dies on it's face when you try to take off"

if it doesn't fall on its face?!?

In any case, carbs usually DO hit a little rich when you mash the throttle open. Just one of the little things that they do.

It dies, not falls on it's face, when the idle mixture is to lean. That's because he thinks tuning the jets will stop the black smoke when you get on it.

I always rich it back up to running ability, but he goes nuts about the blacks smoke, so he leans it till it dies at idle or in drive with your foot on the brake.

Not to sound harsh or put you down, but from way your wording is, you and your dad are all confused about carb tuning.

What I'm reading from your post sounds like yall are turning the mixture screws in and out right?

and yall think thats richening and leaning the carb out right?

Well if so yall are half right..

Those screws are for idle only.. It does not change the rich/lean-ness of the carb after idle. The only way to change that is to unscrew the jets and screw diff sized ones in.

Those screws will cause it to choke and die at idle or smoke like crazy at idle, but does nothing after idle.


To tune the mixture screws you hook up a vac gauge to engine, and tune them to get max vac.

Now if you smoke, bog, or surge, or what ever then turning those screws WILL NOT fix the prob, cause they are adjusted right if you done it with a vac gauge.

You then need to look at the accel pump, pump cam, power valve, float height, and jetting.

There's much more to carb tuning then turning them little screws.

If you already know this, and I mis read your post then I want to say I'm sorry now.

True. The idle circuit and the power/acceleration circuit are separate. Get best lean idle, then tune for power. Jets and power valves, in other words. If it stumbles off idle, you need to go up on your pump squirter. If it blows that black smoke off idle then go leaner on the squirter.

I thought it couldn't just be the jets, but he's convinced it has some thing to do with them, I know they are just fine if not a little small...... It was running very pleasent and he changed them to lower ones, and now it's harder to tune....

However he believes they control every thing, and I haven't been able explain to him they don't, because I wasn't quiet sure what was causing it, I haven't had the time to even look at the carberator.

To me it sounds like what you say, an accelerator pump issue. I didn't know if the power valve would do this, and the more I think about it, the more I doupt it's the power valve.

[This message has been edited by GoodToTheTouch (edited August 30, 2005).]