Slight black smoke on WOT, suggestions?

[lrust]

Cliff,

I finished Dragweek this year (~ 14.5mpg over 900 miles and 5 dragstrip passes with no overdrive w 3 adults and trunk full of luggage and tools).

At WOT during burnout and launch, crewmembers saw momentary black smoke from exhaust.  I launch using footbrake from idle.  Engine comes up to ~4,000 almost immediately from converter before it starts to move the car.  No noticeable bog or hesitation.  AFR from LM2 shows a dip in AFR at beginning of run down below 10 or so but I suspect the sensitivity of the sensor and meter doesn't completely catch the rich condition.  During the run the AFR shows in band through all 3 gears.  455 w 670s and SD OF cam, 3800 lbs w your rebuilt QJet from a couple years ago.  60' time is 1.6x.

I am thinking that I should start by slowing the choke pull off rate?  It is about 1 sec now. Thanks in advance.  I can provide other details if needed.

Thanks,
Lowell

[Cliff Ruggles]

We tune for results not for any particular A/F ratio or seeing a little black smoke out the exhaust.

If the car leaves well, no stumble/hesitation/bog and pulls hard all the way down the track I really wouldn't worry about a little smoke when you stab it hard on the starting line.'

Taking away the needed fuel to overcome a potentially lean condition could bring in other issues.

So basically if the things are working well I wouldn't worry about it.

Related, on several occasions I've changed secondary metering rods back to back to back on private track rentals when I had a lot of time and wanted to do some testing. 

I've ran rods so small the engine was "pig" rich and putting out some black smoke to fatter rods that made it so lean it was starting to surge a bit on the run.  The difference in ET and MPH between all runs was well under a tenth and less than 2mph.  This simply happens because my car leaves really hard with good traction, so total engine power on the rest of the run becomes a smaller part of a big plan.

It also shows us that we really aren't chasing much for ET/MPH on a well tuned engine and well set-up vehicle with A/F ratios.  Of course this assumes the starting point was spot on and not WAY off someplace.......FWIW.....Cliff

[lrust]

ok, thanks.  That is what I thought you would say.  Since all else seems to pull hard and run well that there are not much gains in chasing a little smoke.

Lowell

[Kenth]

The secondary initial POE discharge holes size varies a lot between makes of Q-jets making more or less black smoke when air valves opens.
I have noticed the smallest .029" on Olds units and the largest .078" in early Pontiac units.
Most, if not all, 1975 and later Pontiac units has .063" outlets.
I have also noticed, tuning a marine engine hanging over the carb at WOT, these ports continue to add fuel as long as the air valves are open.