Help...slight hesitation accelerating from idle. Can backfire / stall when cold

[russg]

Car is running great for the most part, just this last little hesitation is driving me crazy trying to tune it out.  383 with 670 Holley SA.  When cold and trying to take off, you really have to feather the pedal to keep it from stalling or backfiring.   Once it's warmed up (at least 10 minutes later) it runs good but there is always a slight dip or miss when rolling slowly and you try to mash it.  If you are stopped and want to give it a good launch, with the brake on you have to feather the pedal until you get past the hesitation and once the rpm's are up past 2 grand no problems, runs like a bat outta hell.   When cruising at a constant speed with rpm's below 2 grand and you lightly push the pedal you'll feel it drop off before it accels again.  The accel pump nozzle is currently a 37 and it pumps a good shot of fuel immediately when moving the throttle.  Car has new plugs which are about perfect color light tan, firecore wires, cap and rotor, msd blaster 2 coil.  Currently timing set at 15 deg at idle. Can the elec choke somehow be a culprit?  Do I need to play with timing? Float levels? Larger squirter maybe?  Could the ignition box be to blame?

[bordin34]

That is exactly what my 670cfm Street Avenger does on my 400. I have no idea why though.

[A383Wing]

First thought here....sounds like it's too lean....I'm not a big fan of Holley....sounds like couple steps higher main jets are in order

[firefighter3931]

First thought here....sounds like it's too lean....I'm not a big fan of Holley....sounds like couple steps higher main jets are in order

Sounds like a jetting issue Russ.

You might have to fool around with the spring in the vacuum pod on the secondary side as well. 



Ron

[elacruze]

Check your rear butterflies to see that they're closing all the way. There's an adjustment for that, if it's open too far you'll be lean just off idle.

[BrianShaughnessy]

Add more choke.

Here's a link to the SA carb manual... see page 8.  http://www.scribd.com/doc/9376128/Holley-Street-Avenger-Carburetor-Manual


If you need to keep the choke on longer cause it heats up too fast...  Holley makes this gizmo that'll slow it down.  http://www.summitracing.com/parts/HLY-45-267/

[dodgecharger72]

My car had been doing this too, but I have an edelbrock. I couldn't fix it for the life of me but when I get it running again hopefully I will figure it out

[russg]

Thanks for the suggestions.  i will check on the butterflies.  Currently have 68 jets up front in the primary side and have a 4.5 power valve.  My vac reading in gear is just over 7.  Here is what plugs look like

[russg]

I went to a 72 76 jet combination and installed a 6.5 power valve.  Seemed to iron out most of the problem.  I was going to try a smaller jump to 70 74 jets but did not have them, should I get them and try just to make sure it may be sufficient?  Don't want to run the other way into a too rich situation.

[elacruze]

Well, your seat is your guide and it sounds like you've got it figured.

My  on the plugs is (if you pulled that plug out after a driveway warmup or short around the block drive) that you have plenty of choke, but the low speed is lean which you just proved out anyway. I like to keep the choke lean enough that in the coldest weather you'll drive in, the car won't drive off for 30sec-1min. Just to stay away from black plugs and carbon. What did you find on the rear butterflies?
It's easy to forget that no carbureted car was ever able to drive away on a cold day without a thought like you can with Fuel Injection. I start it and arrange my seat belts, sunglasses, mirrors etc. while the engine makes enough heat to move out. Warm engines are happy engines.

[A383Wing]

I went to a 72 76 jet combination and installed a 6.5 power valve.  Seemed to iron out most of the problem.  I was going to try a smaller jump to 70 74 jets but did not have them, should I get them and try just to make sure it may be sufficient?  Don't want to run the other way into a too rich situation.

Best would be to take car to a shop that has an exhaust analyzer.... that will tell you which way to go if need be

[Cooter]

Holley carb's are the "heart and soul of Performance", but they are NOT Plug and play carb's that's for sure. If the off idle stumble continues after all else, try stepping up the Acc. Pump shot with either Cam's at the linkage and a larger, EXTENDED squirter....This is like a must when dealing with stumbling Holley's...