Stevemel98

Please Help. I have a 91 firebird. I have installed a 350 with a edlebrock 600CFM performer carb. I have .480int .480exht 230 duration cam. edlebrock performer RPM intake, HEI distributer, 2500 stall converter, and headers. I still have the original 2.73 rear gear(i am upgrading to a 3.73 soon). The problem that I am having is the car runs great on the street but when I am at the track it stumbles at the launch. This is more then just a bog, it fall hard puffs black smoke and sometimes even dies. I can never get it to do it on the street. On the street it will just smoke the tires and go. When at the track if i don't do a good burn out and the tires spin at the launch it will not act up. I can only duplicate the problem, launching hard without the tires spinning. I tried a buddies Holley carb and it worked better, but still had a hesitation at the launch. I talked to edlebrocks tech support and they suggested checking the float levels. I adjusted them as they recommended with no improvement. I also have a bypass style AFPR set at 5.5 PSI. The car really runs great except during hard launches at the track. My best ET is 14.3 @97MPH and 2.1 sec 60'. but most of them are 16-17 @ about 95 MPH with 4 sec 60' times because of the stumble. Thanks for any suggestions.

xpndbl3

iTrader: (5)

isn't there a way to adjust the secondary flap somehow on an edelbrock to get it to open a little later. have you tried just launching off idle and stabbing the pedal at the track, possibly the secondaries are opening slowly while you're standing on the gas and brake to launch and then your bog is related to missing that pump shot since the secondaries are already open. i'm sure the gears will help tremendously as well, try lowering the floats a bit at the track or looping the two vent tubes with a piece of hose, if it has two vent tubes like a holley, I know that helped a bit on one of my engines when it would stumble. I am sorry that I'm not all that familiar when it comes to carter/edelbrocks to point you in a better direction.

contact

I would suggest,

try less pumpshot,
try some 'right foot disipline',

problem might be, metering rod going into 'power' mode,
when, for other reasons, you have too much gas already.
if so, you will need to monkey with the metering rods
and/or springs

ZEEYAA

Im not familiar with the edelbrock, but if it were a holley then I would maybe adjust the secondary pump shot cam, where it cam in alittle sooner, sounds to me that you have a lean problem on your secondary. And as stated you may already be pulling from your pump shot if its adjusted too tight, and then when you really need it, it may already be dry. I dont know how that interacts with the edelbrock but I think you may need to delay tip in.

sofakingdom

iTrader: (1)

There's your primary clue, right there.

It's obviously not a "lean" problem. You clearly have TOO MUCH FUEL.

If you get a good burnout but then it does this when you try to leave the line, and DOESN'T do it when you don't do a burnout, then it's probably because the fuel bowls get over-filled during, or while recovering from, your burnout.

I'd start by backing the fuel pressure off; try 4 lbs or something, and see if it's better.

Carbs don't need "fuel pressure". They need FUEL DELIVERY. Meaning, if the fuel sysem could deliver enough fuel at ¼ psi to keep the bowls full, the carb wil be happy. The FP itself doesn't participate in the carb's operation in any way. It's not like FI where low FP will create a lean-out. You CERTAINLY DON'T need 5½ psi with that little bitty carb that's too small to begin with, as entirely enough fuel to match the amount of air that it can admit, will be able to flow through its needle and seat at a much lower pressure than that.

I also don't see it as a "hard launch" issue, like all the fuel sloshing somewhere or that type thing. 2.1 sec short times isn't what most people would call a "hard launch". Lots of people use those carbs and get satisfactory results with MUCH QUICKER 60' times than yours, so it's definitely possible to get better results than you're getting, without changing carbs.

F-BIRD'88

Recurve the distributor for more initial advance but same total advance. try 24 initial @idle (700rpm) and 34-36 total. (limit advance travel from stock 20-24 deg to about 10-12deg travel)
Change the power step up spring to the 4" vac one. Cleaner idle.
Get some different accelerator pump shooters.
Install a heat insulator gasket (wood) under the carb. Edelbrocks tend to suffer from heat soak. A hot day in the stageing lanes at the track will cause this. The fuel in the bowl gets over heated. when you go to launch the car it initially stumbles till the hot fuel is used up.

Raise the idle speed (stageing rpm) to about 1200rpm to launch the car cleaner.

AJ_92RS

I once had a '71 Nova that did that after I switched from a Holley 650 VS to an Edelbrock 1407. FYI, this car had a 350, single plane intake, Crane 302 * Fireball solid cam and Muncie M21 with 3.42 rear gears.

The Holley never did bog off the line. The Edelbrock did with more than 1/2 throttle.

Just out of curiosity I switched the vacuum advance from one port on the front of the carb to the other. The problem went away.

I wasn't sure which was ported and which was manifold vacuum, but since the Holley's port on the side of the front metering block is ported, I assumed that's the one I wanted to use, but didn't at first.

Later I found out I had put the vacuum advance on the manifold port on the Edelbrock. The guy I was talking with told me that after I stabbed the throttle, the vacuum dropped out and I lost the advance the timing was spinning at. That combined with the accelerator pump shot caused a lot of fuel to dump into the engine and bog it down.

Made sense to me since after I switched it to ported vacuum I didn't have a bog anymore.

So basically, try that.