6pak tune help

[70gtx]

where do i look first. if i punch it and then let off it runs rich and i get black smoke from exhaust.can be from stand still to 1/8 mile run, when i let off it sputters for a few seconds till it burns fuel up.the center carb has 76 jets which has border line rich when we dynoed motor. should i try 74s or is it the outters staying open to long(light springs right now).
i have no hesitation right now and it runs good other wise.
but did foul plug today ,plugs look on the blackish side.im getting hotter ngk plugs for it but i dont think that is problem.
what do you think and where to look first?

[70gtx]

any carb people out there?

[DAVE JONES]

Dont fret doc, I dont think anyone is ignoring you but your title regarding 6 pack tune scares alot of people from replying since they dont think they know how to tune them, when in fact, they really do but just dont know it. They forget that instead of just 2 secondarys, there are 4. I'm not a carb guru like your looking for but I do run a 70' 340 6 pk and have had similer problems. First, Your idea of going to a hotter plug will probably help. Your HP being in the +600 is impressive so I cant talk apples to apples but I would try the plugs first, Then start bringing the jets back. I really dont think your 2ndary springs play into this at all. If you get no bog off the line then you have them setup properly.
The hotter plug should be able to utilize your rich condition better. I'm assuming that since your experienced enough to run a 600+hp 6pk, you've already qualified some of the other variables that could cause this including making sure that your ignition is setup properly to burn the fuel.
I know of a couple of carb gurus on this site but they dont post everyday, maybe once a week so stay tuned and wait till they review this......good luck.........dj

[70gtx]

thanks dave, i slept on it last nite, it cant be the outters flooding me because the vacuum closes the butter fly's. im using 50cc accelerator pump with yellow (whatcha call it).im going to fool around with a different color and back down to 74 jets.
my car will start up and run cold quite good at 63 degrees as long as im off idle circuit with no choke and no hesitations . so im sure im a little over fueled.
i pulled ngk plug and i got coldest plug so i ordered 2 sizes hotter as my dyno man said shouldnt be a problem ,as aluminium heads absorb so much heat.this will be the hottest plug for the indy heads.

[DAVE JONES]

As far as your yellow cam pump...... Personally I would leave it alone for now. My experience with cam pumps varies but it regulates the inital blast of gas.....how much and duration during the initial stomp only. Since you mentioned that there is no bog off the line, you probably have it dialed in right. I'd look to the other avenues first.
If the puff of black smoke is off the line and not during exceration then your shooter may possibly be a touch big but again, you say your smoke is after the run during decleration and not off the line.........dj

[Karl43]

Try smaller jets and smaller squirters. Change only one at a time to make sure that one does nto make it run worse.

[70gtx]

i talked to holley.that guy sayes i must have fuel running over during acceleration, but it also shutters around 3200 rpm in the garage holding the throttle still,he said to lower float ,but could be from any one of the carbs . guess ill try one thing at a time ,lower floats,lower jets,maybe tryaccelerator pump cam. let you know what i find soon.

[DAVE JONES]

Disconnect the outboards and tune the center carb. Only and I mean only after the center is adjusted so your current problems go away, should you then concentrate on the outboards.
Besides duing a garage tune up by ear, make sure that you do some runs with using just the center. adjust the pump cam, shooter, and jets. Make sure that when you change the setting of the pump cam or the cam itself that you reset the accelerator pump arm. Alot of people dont realize that this is the only way to see the true cam affect and with out doing this adjustment, you'll make bad decisions since the cam wont work properly. After this is all done, then hook up the outboards and set them up. The rest is history. ...............dj

[DAVE JONES]

I forgot to mention, I didnt hear you mention anything about your power valve. Make sure its the correct size for your vaccum reading.

[70gtx]

sorry to hear about your motor dave, yes im going to give it a try tommorow if i get time. im running 6-7 vacuum idle and 4-5 in gear ,i now have a 4.5 but im going to put in a 2.5 while ive got it apart.